I've been using css based templated nearly for 2 years now. It is not really hard to accomplish removing all the tables and maintain the style. But if you are an upgrade maniac and try to follow every vBulletin upgrade you'll hate Jelsoft on each upgrade
Thats why i usually donot upgrade to latest versions and on each major release instead of working all the templates i decide to create a new style from scratch. But i never care to keep the look of vBulletin as i dont like it at all and without very carefull eyes my styles cannot be recognized as vBulletin ( the current one i use is half way done and it has the closes look to vBulletin )