Reply #2: Here is what Cornell says:

[acmejack]

Ultra-Pasteurized Milk: “Ultra-Pasteurized” means that the milk is heated to a minimum of 280°F for a minimum 2 seconds. This temperature and time combination is much more lethal to bacteria, killing virtually all of concern in milk. Ultra-pasteurized milk is also packaged under near sterile conditions, which makes recontamination with spoilage bacteria unlikely and rare. Though Ultra-Pasteurized milk is processed to be free of spoilage and harmful bacteria, it is not considered sterile because it is not hermetically sealed (i.e. canned), thus, it requires refrigeration. Ultra-Pasteurization is most often used for creams and specialty dairy products though its use for milk is becoming more popular. Ultra-Pasteurized milks will often have more of a “cooked” flavor when compared to conventionally pasteurized milks. The average shelf-life of Ultra-Pasteurized milk products is 30-90 days when held under refrigeration, but only until the product is opened. Once an Ultra-Pasteurized product is opened it may become contaminated with spoilage bacteria. Thus, after opening, Ultra-Pasteurized milk should be kept well refrigerated (34-38°F) and consumed within 7-10 days for best quality and taste.

http://216.239.51.104/search?q=cache:z-YAYcTnI94J:www.foodscience.cornell.edu/mqip/FACTpast-up.doc+ultra-pasteurization&hl=en&gl=us&ct=clnk&cd=14&client=opera

also from Horizon Organic Dairies "UP and HTST milk have the same great taste and nutritional benefits, but UP has an extended refrigerated shelf life (before opening)"

http://www.horizonorganic.com/site/faq/products_org_milk_process.html