Just upgraded my Hardy installation to Intrepid Beta for kicks (Slow Sunday).
Will probably do a clean install later.
Quick take
Pros:
Love the new tabbed nautilus interface
Much needed eject button next to drives in the places menubar (left of nautilus)
NetworkManager works prettier, switches very seamlessly between wired/wireless.
Suspend/Resume is faster (old acer laptop intel915 GMS chipset, Centrino,2 GB RAM)
Cons:
Pulseaudio !!! Doesn't let me play any sound. Possibly a configuration issue. killall pulseaudio reverts audio to normal. Don't have any fancy sound HW. Mike works crap (always did, even for Hardy, works okay in windows).
Update : Pulseaudio has mysteriously fixed itself (lots of patches being downloaded everyday). Works perfectly. Also be sure to try the new Ubuntu dark theme. I like.