I'll do this without quoting Dinsdale; it makes for a much more orderly post.
Ice and food preservation
Pepper does not preserve food very well. Neither does saffron or other expensive spices. Salting and smoking meat preserves meats, honey can preserve fruit, cheese-making 'preserves' milk. All those methods were used in medieval europe. Pepper a steak heavily, leave it out in a non-freezed temperature(belowground you can get it fairly cold) for a month, and try it out. I have witnessed an extremely enjoyable event in which a lecturer of medieval history, who had been teaching us that medieval people 'used spices to mask the smell of bad meat', being given a hunk of bad lamb, heavily seasoned and grilled, to eat. Cue a weeks absense from the university due to diharrea. After this he wasn't all so certain about the theory. I have not seen direct evidence of ice houses outside scandinavia, the mountain regions of europe russia, england and the northern baltic coast, but ice was cut and exported; at the wedding of the Duke of Burgundy in 1468 we have extensive supplies being procured for the cold food.
Medicine
Very few medieval sources compare frankish and arab medicine. The amputation described by Usama was indeed a common operation until very late, but amputations were performed in the arab world as well;
I am not declaring european medicine to be superior. I am protesting the common view on western european medicine being drastically inferior to arab medicine by the time of the crusades. Cordoba had centuries of tradition compared to Salerno(and experimental medicine was uncommon even there)
For Usama's text; here is an excerpt; the text after the malpractice example:
(
http://www.fordham.edu/halsall/source/usamah2.html)
"I have, however, witnessed a case of their medicine which was quite different from that.
The king of the Franks bad for treasurer a knight named Bernard, who (may Allah's curse be upon him!) was one of the most accursed and wicked among the Franks. A horse kicked him in the leg, which was subsequently infected and which opened in fourteen different places. Every time one of these cuts would close in one place, another would open in ancther place. All this happened while I was praying for his perdition. Then came to him a Frankish physician and removed from the leg all the ointments which were on it and began to wasb it with very strong vinegar. By this treatment all the cuts were healed and the man became well again. He was up again like a devil. Another case illustrating their curious medicine is the following: In Shayzar we had an artisan named abu-al-Fath, who had a boy whose neck was afflicted with scrofula. Every time a part of it would close, another part would open. This man happened to go to Antioch on business of his, accompanied by his son. A Frank noticed the boy and asked his father about him. Abu-al-Fath replied, "This is my son." The Frank said to him, 'Wilt thou swear by thy religion that if I prescribe to you a medicine which will cure thy boy, thou wilt charge nobody fees for prescribing it thyself? In that case, I shall prescribe to you a medicine which will cure the boy." The man took the oath and the Frank said:
Take uncrushed leaves of glasswort, burn them, then soak the ashes in olive oil and sharp vinegar. Treat the scrofula with them until the spot on which it is growing is eaten up. Then take burnt lead, soak it in ghee butter and treat him with it. That will cure him.
The father treated the boy accordingly, and the boy was cured. The sores closed and the boy returned to his normal condition of health.
I have myself treated with this medicine many who were afflicted with such disease, and the treatment was successful in removing the cause of the complaint."
Usamas conclusion is, as is his conclusion to the entire matter: Frankish medicine is
curious , strange and not like his; but not necessarily insane. He is most disturbed not by their medicine but by their treatment of their women:
"The Franks are void of all zeal and jealousy. One of them may be walking along with his wife. He meets another man who takes the wife by the hand and steps aside to converse with her while the husband is standing on one side waiting for his wife to conclude the conversation. If she lingers too long for him, he leaves her alone with the conversant and goes away. "
He then cites several examples of franks being 'devoid of jealousy'.
Sanitation:
So soap wasn't common in europe? Hmmm. Soap had been around in europe since the celtic iron age and certainly did not suddenly disappear with the medieval period. Use of the soft soap was massively increased in europe in the ninth century and grew ever since; soapmaking guilds were abundant in medieval europe. HARD soap, on the other hand, was imported from the arab world in the ninth century and made in europe from the 12th.
As for bath houses, well, Paris had 300 of them in 1223; they are frequently reviled by clergymen as sources of illicit sexual encounters in later eras, and mentioned in the 'Roman du Rose' and the 'Romance of Alexander'. Saunas were extremely common in the northern world; in the 'sverrirsaga'(describing early 12th century events) some men are ambushed in the sauna and have to charge Sverre's men naked. Larger public baths were usually of roman descent; Charlemagne had one at Aachen and the Aix-les-termes of southern france is mentioned in the Inquisitorial protocols (of Montaillou) of Bishop Jaques Fornier, but new ones were also built. Bathing is presribed as healthy in the Book of Manners, the aforementioned Book of Health and illustrated in countless medieval manuscripts(the Codex Manesse and the Maciejowski Bible to name but two). There are few 11th century illustrations of bathing, but then again there are few 11th century illustrations of anything regarding private life.
The personal hygiene of europe in all likelyhood decreased in quality after the renaissance(
http://www.womenshealthpc.com/11_00/pdf/816LookBack.pdf). Increased imports of perfume, increased washing of clothing and the bad reputation of the public baths led to a decrease in human cleaniness.
Immigration: We do agree. I wrote 'religious OR commercial reasons'. The land issue is of course also relevant, but mostly for the upper classes; settlers had little land in the middle east to claim; the area was more heavily populated than western europe.
Whether more time would have allowed mass emigration is uncertain but in my mind doubtful. Other areas were far more attractive for emigration. German and Scandinavian settlers went east, England wasn't fully developed until well after the crusading period, and french settlers also moved about internally. There was a lot of unfarmed land in europe in 1066, though of course this decreased with time. The middle east was already chock full.