I use a GPLv2-only licensing in some parts of my RSS Reader application. Now I just recently got a note from Debian's Hubert Chathi via E-Mail that this license is - fasten your seatbelts - incompatible with LGPLv3. In short: When shifting from GPLv2 to GPLv3, the FSF managed to change the x-GPL licenses in such a way that GPLv2-only applications automatically become incompatible and thus illegal-to-link with whatever LGPL3-framework they're using. Words fail me when trying to comprehend these licensing politics.
This will make me think twice about whether GPL is a good choice for future publishing of source code.
Update: (June 9th 2008) For the release of the next stable GNUstep release, the project temporarily reverted its license back to GPLv2+. Link, Link. Here's the original discussion about the GPLv2 licensing issues on the GNUstep developers' mailing list. (This linked message also contains a list of the GPLv2-only-licensed projects causing these problems. Regarding the low overall number of GNUstep applications, this number is quite impressive.)