There are no expectations. Some things (like a theme) are done for personal use and then shared. Some things are may-complicated and require tons of time and skill to produce, like Preware, WebInternals, QuickInstall, etc.
Personally I like to send $20 when I make a donation for the big stuff like Preware, 800Mhz Kernel, QuickInstall, Internals, etc. There are hundreds of man-hours in each of those, and they are some of the best engineered and best executed elements I've ever seen.
These guys give their own time, buy their own equipment, coordinate their efforts, and provide 24x7 support in these forums. The way I look at it is that I'd pay $10 or $15 for a great app or a great game. If I want MyTether support, that's $15. So I think each of us should donate generously, especially since most users won't donate at all.
And when they do a major upgrade because of a new WebOS update, I think we should donate again...
They don't take donations to make money (if the point was money, they would just charge for this stuff) they do it to benefit the community and advance the platform to prove the potential they can see in webOS.
The least we can do is help them cover their costs. The 800mhz kernel has been downloaded more than 15,000 times. I'm sure it's even more for Preware and other items that have been around longer.
Imagine if everyone donated $20 to at least one of those developers? We'd see a lot more iPhone developers over here, and less stress on the developers we have now that are spending their personal resources to build the stuff we are enjoying.
Give often, and give generously. I think we sometimes take for granted just how good the stuff is that we enjoy from the WebOS home brewers. IMHO