Hey guys - don't despair. I also had the same problems, and thought I'd pull my hair out, and revert to SL. I managed to fix things, and I haven't had a crash since. I agree though; Lion was pretty frustrating for awhile.
In my case, there were incompatibilities. It seemed random for the most part (it often hung at the startup screen, but it could happen at any time), but Safari was often involved.
My recommendation: go to the Apple menu, and select About This Mac > More Info > System Report. Go down to Software, and click through each of the subheadings, looking at the "Kind" column. Look for any leftover PowerPC or Classic apps - they're trouble.
To fix things for myself, I used terminal to rename the Library folder in my home directory, and in the global directory (just to LibraryOLD), and immediately rebooted. This will make things look pretty strange and may cause some apps to not work properly...but it will also help you to discover what's causing you grief. Try using the system for awhile and see if there are any crashes. If things run smoothly, you can begin adding back in. Lion will create new Library folders, and from there you can decide what to return. Use common sense and put back folders that couldn't possibly be responsible first. Chuck the cache folders. Folders that are often naughty include fonts, startup items (startupitems, launchagents, and launchdaemons), internet plugins, contextual menu items, screen savers, quicktime, and preferences. Each time you replace a folder, reboot and check the solidity of the system.
I know this is a long tedious process, but it's worth it. It will rule out hardware issues, too. To save a little time, you can restore several folders at a time. For example, put half of the folders back where they belong and restart. See if the issues remain. That way you can narrow it down a bit faster. I would however, recommend doing the folders I listed above individually.
Hope this helps.