Just want to say that I’m currently working hard on a beta release of WatiN 2.0 somewhere in Q1 of 2009. It will be a major upgrade to the current CTP 2.0 versions and will basically give you the same functionality to automate FireFox and IE as version 1.3.0 offers for automating IE.
So no concerns there.
Hope this helps in making your choice
Jeroen van Menen
Lead dev WatiN