One thing that will definately improve in Drupal 6.x and onwards is the performance relating to database queries, It is not uncommon for a site which has the usual formula of a few views generated blocks, translation module and a couple of other miscellaneous views entries to suddenly push your site into the 200 to 600 database queries just to generate *one page*.

Fortunately Drupal is continously improving with its caching methods and data abastraction models so it doesnt always have to hit the DB for something simple, or get it to return multiple items in one hit, but i digress.