it's slow, full of idiotic "quirks", it doesn't maintain reliable dependencies, it is very very expensive, there are a great many useful Oracle features that just can't be supported using it (merge, insert /*+ append */ , bulk updates, insert into .. returning etc.), it's a bastard to debug a complex mapping blah blah blah. The metadata reporting functionality is abysmal -- it's there as a marketing tool only, according to informatica tech staff.

I've been using it for over four years now, and i dislike it more and more.