The current state of marketing automation

We've been doing a lot of research into marketing automation and would like to find out what other's have experience within this area. Eloqua, Pardot, SilverPop, and Marqui are all companies that have a good grasp in this area, being able to rate leads and build drip campaigns through web, offline, and email. They all also sound good in their marketing and sales. However, we know there's got to be some "gotcha's" and would really appreciate your insites before we convert with one of these groups.

Thanks!