I installed Lion and have lived to regret it. I'm OK at this point, but it was a bit traumatic at first.
Like a dope, I didn't do any reading about compatibility of applications and devices before upgrading. I just decided one day, "Well, Lion's been out for a while, and it's not expensive, so why not install it and be current with my OS?" Big mistake! I lost access to Photoshop CS2, MS Office 2004, and a couple of lesser applications -- only the newer versions of those work with Lion!! Arggh!!!
And, even worse, my Logitech trackball quit working, so I was forced to go back to the piece-o'-crap Apple "Magic" Mouse, which in my experience constantly lost Bluetooth connectivity and needed fresh batteries every day to be even somewhat reliable. I finally broke down and got a Bamboo Capture, which I like a lot -- although I wasn't thrilled about being forced into it. (Again, my fault for not investigating, but it's always a frustrating experience for the user.)
Instead of MS Office I'm now using Open Office, which works great, is free, and is totally compatible with MS Office as near as I can tell. For images I'm using both Pixelmator (only $30 and a very good alternative to PS) and Photoshop Elements (got a free copy of that with the Bamboo tablet). PS Elements 8 includes everything I was using in CS2 anyway (comes with Adobe Bridge also), so I'm once again a happy camper.
And I've learned my lesson about verifying compatibility with favorite apps before upgrading the OS!!