cmj : "Which version of the libraries do you link against? will they still be there in the next release? are they the same on debian/fedora/suse?"
This is a good point (and I won't even go into Debian being so far behind sometimes it makes Win98 look like a modern OS at times). I would imagine that linking against wx2.6.2 (the current version) and supplying a custom build (which won't break when 2.6.2 changes) is probably the best way to go.
You're right about the moving target. However, now that Mac OS X is BSD with a fluffy front end, you can probably include them in that statement (albeit not moving quite as fast).
FC5? I'm still testing FC5test1, the full release isn't due out for a couple of months yet!