...There's some kinda word going around (ask Peter) about some problems with exim4 and SpamAssassin integration, but I'm not up on the details thereof. I've got work to do and such.
Meanwhile, I run exim4 at home as my only MTA. The *BIG* change that I noticed from exim (version 3.x) to exim4 is that instead of one huge-ass monolithic config file, there's a whole directory tree of smaller, more-easily-managed configs. This is a GOOD thing, as the exim3-style exim.conf was a fucking beast, and that's putting it nicely.