Somebody wrote to me the other day asking about how/whether they could memoize Locale::Maketext language handles in a mod_perl system they're writing under. I said how (altho the speed benefits are probably miniscule), but I also gave them my standard advice on such matters, which is this:
If you're worrying about page load-times, install mod_gzip before you start fretting over optimizing Perl. Secondly, tell your web designers to buy, read, absorb, and obey Zeldman's book Designing with Web Standards. This is not about fretting over HTML/XHTML distinctions, but about using CSS instead of <table> abominations. Using CSS in new pages/sites, instead of using table hell, will make your HTML saner for the programmers to deal with, and faster for transfer.