A small note: if you are using Lightning for Thunderbird and you install or upgrade to Ubuntu 8.04 (Hardy), you might run into an issue of you calendars disappearing (probably only when using the build from the Lightning website):
Error: [Exception… “Invalid ClassID or ContractID” nsresult: “0x80570017 (NS_ERROR_XPC_BAD_CID)” …
…/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/components/calItemModule.js
Line: 67
This is related to the fact that Hardy upgrade the C++ libraries to libstdc++ 6. In order to fix this, you might want to try installing the 5.x version of libstdc++.
Another goodie: starting with Lightning 0.8, WCAP support for the Java Calendar Server is now part of the main trunk.