True all new OS's have their bugs, since it is impossible to test every possible configuration, but Lion seems to have more than its fair share of performance bugs.
Overall, I'm not as concerned with the performance bugs in Lion since I know Apple is working on fixes for them.
My concern are some of the new "features" of Lion that either remove functionality or can't be turned off. For example, the downgrading of Spaces and Expose, the near uselessness of a 2nd monitor in Full-screen mode, the loss of "Save As..." and "Do You Want to Save?", and the lack of control over Resume, Versions or AutoSave.
I hope Apple is also working on restoring or gaining these functionalities while keeping new features that some do like, i.e. Mission Control. Some like it and some don't. I would prefer the SL's Expose/Spaces, but the sign of a good OS is the ability to be used in different ways by different users.