Personally, I usually wait until Alpha2-Alpha3 and get "bored" of my stable system and upgrade... But given the amount of serious overhaul going on in the boot process still, I would try and persuade you to hold off, perhaps until beta.
A good way to get a good health-check on the current version is to hop into irc://freenode.net/#ubuntu+1 and see what people are complaining about. Same goes for the Lucid development forums on UbuntuForums. If you've got concerns about a specific bit if essential kit (graphics, wifi chipset) ask.
And if you do take the plunge, back up. I know it's said everywhere but it's parroted so much for a reason. Data loss hurts in a way no physical affliction can.
If you're not experience with running an unstable system (and they can take some taming), do as matpol says and hold off until a month after release. You'll have plenty of community support from people with similar hardware (something that is vital if you're having weird issues).
Do you have to worry about things you've built: of course. System dependencies change, old things will be cleaned up and self-built things don't have their dependencies stored in the package manager so you might have issues. If you're organised, you'll have all your source in a single place so you know what you need to build if things don't work.
Is it worth it just for the theme? No. You'll appreciate it a lot more when it doesn't nuke you're system in a couple of months time.