Well... I have it, and have not had any issues with it whatsoever. I would say some of the downsides are the fact they have reworked some of the structures. Add Remove Programs is now just Programs and Features. User information is now is /Computer/C:/Users/Username which is different the C:/Documents and Settings/.....
Now, the parental controls they have done a wonderful job on. The interface is pleasing. The sidebar with gadgets is pretty cool.
If I were you, I wouldn't go out and buy it, I'd wait until the next time I upgraded. OH... and I am a Microsoft Certified Technology Specialist in Windows Vista, so I should know.