I installed Lion, and I'm generally happy with it. But I might replace my mouse with a trackpad so as to take advantage of the shortcuts that the multi-touch gestures provide.
One thing I definitely don't like about Lion is the appearance of the GUI for iCal. It now reminds me of the calendars office workers used on their desks after they switched from ink blotters and fountain pens to ballpoints and Biros. It doesn't interfere with the functionality of the calendar app. It just looks bad. And it could well indicate the future graphic design direction for OS X.