I recently obtained an Intel Mac running Leopard; my old computer was a G4 desktop running Tiger (OS X 10.4x). Apple’s Migration Assistant happily transferred my old app’s and data files, so I was running Thunderbird 2.0.0.19 on the new machine just as on the old one, including settings, messages, add-ons, etc. I had been accustomed to Thunderbird periodically checking for updates and informing me of such, then installing them. I had seen no notifications since running TB on my new Leopard/Intel machine. Note that in Leopard what one sees in applications has changed to integrate the help system with Leopard’s built-in Spotlight search software. Just by coincidence in viewing a Version Tracker page I became aware that there was an update of TB to 2.0.0.21. Curious as to why the TB copy on my new machine hadn’t alerted me of this, I discovered that the "check for updates" entry was grayed out, and in the Preferences the check-mark for "automatically check for updates" was similarly grayed out (though there was a faint check mark in the box). Ergo, TB 2.0.x.xx can no longer automatically check for updates under Leopard, at least if my machine is any indication. Therefore, other Mac Leopard users who encounter this will have to periodically visit Version Tracker to get updates.