update: novak has pointed out the easier "standard without chat" link at the bottom of your GMail inbox that will completely disable the chat functionality (including annoying popups).
GMail Chat has finally migrated to all of my GMail accounts. I don't really plan on using the chat functionality, so mostly I'm annoyed as the update also includes a popup window that appears anytime you hover over someone's name. It seems really, really, silly to me to see an "Invite to Chat" button when I hover over an Amazon purchase confirmation.
If you're as annoyed as I am and you have Firefox+Greasemonkey installed, Garett Rogers has written a Greasemonkey script that banishes the popup to the netherworld.
Warning: it eliminates all popup windows, including the one for the Quick Contacts pane. The popup window in the contacts pane is the only way I know managing your Quick Contacts, so if you still need to use the chat functionality you may wish to do without.