HW: Dell D430 Latitude (not the best test case, but a common business machine)
I've been running Intrepid for a while now without too many issues. Sure, there's your usual "gotta find the latest drivers after install" for some things such as the wireless. However, "upgrading" to Jaunty has caused MANY regressions for this hardware.
I had to downgrade the video card driver thanks to this bug:
I have yet to get bluetooth audio working through Pulse even though, while a bit sketchy, I could actually use my BT headphones on Intrepid.
Docking with multiple monitors always required disabling and then re-enabling one of them to get it to show and that hasn't changed.
All in all, while I like the improvements, I am debating reverting to Intrepid. I'm not terribly keen on the format/reinstall option, but it may end up being my only option if I want these features back.
I love Ubuntu. I really like Intrepid and Jaunty was interesting enough to make me want to upgrade right away. I was led to believe the HW support would be better in it. It's definitely a regression for my system...