Matt,
I guess one piece of advice I'll offer for free, for whatever it's worth, is to try stuff yourself: there ain't no better way to learn stuff.
Scott (and others advice) of preparing a starter is good karma. Starters are good.
To cast aside my former attempt at brevity.
Rehydrating your yeast can be beneficial if done properly. My experience is that many more people actually screw up the process than do it properly.
The two main things that people do wrong are toss the yeast into water which is too hot and leave the yeast in the water for too long.
Many packet instructions say add the water to warm water. What the hell is warm water? 25 C, 35 C, 45 C. For my money the temperatures quoted by Palmer are too high <SHOCK
HORROR> My understanding is that 40 C can kill yeast. At any rate, a temperature much closer to fermentation temp seems much more sensible to me. It may be that the yeast is better able to rehydrate at a slightly higher temperature, but I say what the hell, the lazy yeast would work if I pitched them at fermentation temperature and I rate any advantage as comparatively small.
If you leave the yeast in your water for too long, how long is too long, the answer is I dont know, but I do know that after rehydration occurs (I think Finite mentioned the small space of time) the yeast does some other stuff - it checks out the environment, can I cope with this pH, what food is around, what enzymes do I have to make - this and other stuff starts happening pretty much straight away. The yeast is gearing itself up for a life in a the cup of water and thats not a life you want to impose on your yeast, you want your yeast to prepare to ferment your wort and make your beer, not mooch around wondering what the hell has changed yet again and deciding if it can cope with the change when you get around to pitching it in your wort.
Now, there are exceptions to this. If you are using Nottingham dried yeast I am given to understand that it very important to rehydrate the yeast. It is the only exception I know of. Certainly Saf and Munton yeasts work well without rehydration.
I'm not a fan of the proofing thing. Proofing was a necessity in the past when the quality and reliability of dried yeasts was in question. Checking that your yeast, whose viability might have been crap to start with, was in a fit shape to ferment your beer after sitting in a supermarket warehouse over a 40 C summer was just commonsense. Nowadays the viability of dried yeasts is much greater (as is their purity btw) and any reputable supplier will have stored them much better than THE OLD DAYS. I think that my contention that proofing is a hangover from the past is also born out by the advice, oft given, of using sugar to perform the proofing. For the reasons given above, firing up the yeast with a balanced profile of sugars (maltose, trimaltose, blah, blah, blah) makes much more sense than the nutrient poor household white.
Proofing seems to me to be unnecessary step, that if you were prepared to do, would be much better replaced by making a bona fide starter.
Quality dried yeasts will work consistently well WITHOUT rehydration.
Happy Brewing,
Keith
ps In the interests of full disclosure, please be aware that I work on a part-time basis at my local home brew store, and that I have, from time to time, sold quality dried yeast.
