<p>GDB has severe issues when debugging with multiple threads (pthreads).
Are there any other good multi-threaded debuggers for C/C++ on *nix?</p>

From my search, I have not found any good multi-thread debuggers for *nix. GDB seems to be getting better, and the last time I had to debug a multi-threaded application on FreeBSD (7.0-RELEASE) it behaved fairly well, letting me find where the error was.