I truly love VIM - it's one of only a handful of applications I've every come across that make you feel warm and fuzzy inside. However, for PHP development, I still use PDT Eclipse although I would love to switch.
The reason I can't quite at the moment is the CTRL+SPACE code-assist functionality that I rely on so much - it's so useful, especially when type hinting, or using PHPDoc variable comment blocks.
I know there are cool plugins for VIM out there that can probably replicate this functionality and then some - but what are they?