Lightning (the calendar provider for Mozilla Thunderbird) finally has a release out for Thunderbird 3.0 and all it's sweet, sweet tabs. When I installed it, though, I got the same error that's covering the Lightning add-on project page comments:

"Lightning could not be installed because it is not compatible with your Thunderbird build type (Linux_x86_64-gcc3). Please contact the author of this item about the problem."