If you're talking elite sprinter such as Ben Johnson, adding 50lbs to his squat or deadlift may not make as much of a difference as adding 50lbs to that of a high school sprinter. Strength is an obvious benefit, but power if of foremost importance (after good sprint mechanics of course). In the less experienced sprinter, plyometrics are probably necessary (more so than in the elite) to condition the tendons for the stress that sprinting puts on the body.
Lots of good information on the Charlie Francis board. Charlie's "Train for Speed" is an excellent (albeit long and sometimes boring) read. I'm planning to run in the 100, 200, and possibly 400m in next July's Bluegrass State Games and am using some of Charlie's stuff to setup my SPP training. Hopefully I can bring home the gold (I think there are only about 4 entries in the 25-29 division).