I'd probably second that, although there could be a case where db would be better.
Not in any of my configs, though.
AAMOF, on my boxen, the best place is /usr/local/share/pear/... the "include" dir --- makes templates and libs available to every site on the host. No fritzing around with path problems when I use include(). Of course, nobody else has access (much, anyway...). Or, so we always hope, heh heh 🙁
It's possible that db would be better if you have a very, very very, fast db server connected to your webhost with something like Gigabit Ether, whilst your local file system was loaded up processing session transactions or something...that's pure conjecture, of course, and something I've never seen, but it might be possible.