I use wikipedia all the time. The entries relating to science are generally the most accurate of all because they've been written by professionals (as opposed to an entry on, say, Britney Spears, that might have been edited by a 12 year old). I've found the text to be very reliable and well-written. Most medical textsbooks are often written poorly with convoluted, long-winded sentences. Wikipedia never seems to go down that road.