Anecdotal evidence: I'm currently using a multi-threaded perl/XS program that uses DBD::mysql 4.004 on several MP machines including an 8-core linux x86_64 box. In this program each thread (between 4 and 16 threads depending on configuration) creates and uses its own database handle.

Although there are still some issues with shutting down the program cleanly, they don't appear to be database related. In any case, it'll run just fine for days without any issues. Note that we create the threads ASAP and then keep them during the whole time the program is running.

The program doesn't really make heavy use of the database, though - most of the work is spend in fairly memory / cpu intensive calculations in the XS code, with the database acting as a dumb (single table) system to store the resulting data in).

YMMV,

Joost.