The Eclipse Web Tools Platform Project has released WTP Milestone M4 yesterday. It was built against the Eclipse SDK 3.1M6 release, which was released about a month ago.
A few months ago, I tested WTP M3 in conjunction with Eclipse SDK 3.1M5, but it wasn't quite there yet... Two weeks or so ago I installed the latest nightly build of WTP M4 on Eclipse 3.1M6 on my home machine, and this already looked very promising, although I haven't had much of a chance to really exercise it, and I didn't quite dare to install it on my PC at work. Now that there are at least official milestone releases for the latest WTP and Eclipse builds, I think I'll give this a try.
To be honest, I don't really care about the app server integration features of WTP, as I prefer to handle deployment and related issues using Ant, outside my IDE. But at least being able to edit JSPs with full support for syntax highlighting, code completion, etc. is a feature that I consider absolutely essential, and this seemed to work very well when I tried it a few weeks ago. Maybe not quite like IntelliJ IDEA, but it's definitely a huge step in this direction.
I'll let you know how it goes.