I upgraded over lunchtime this afternoon and so far it seems ok. There were several extensions that claim to not be compatible but I’ll be forcing the ignore version check using the Mr Tech Toolkit Extension. To disable the version check, click Tools/Mr Tech Toolkit Settings, select the Miscellaneous tab, XPI Install Options and then uncheck “Enable Addons Compatability checking” and optionally enable “Disable XPI install time delay” so you don’t get bugged by the delay each time you want to install an addon.
The plugins that didn’t work were Better flickr 0.3, better gmail 220.127.116.11, Better greader 0.6.1, bit.ly preview 1.262, firebug 1.3.3 (upgrade was found to 18.104.22.168b), Microsoft Net Framework Assistant 1.0 and New Tab King 1.9.7.
Both Bit.ly, and New Tab King seem to work – I’ve not tried the others yet as I now have to get back to work.