I agree qith cfx211 - Kudos to Receptional for starting this great thread.
That's why I say DIY. Only you can know what is critical for your business. It sucks to shell out money for a product and find it can't meet the one or two critical issues you have.
That's what struck me in that article on inc.com that I posted above. Each of those companies:
Use tracking in one shape or form
Built their systems themselves
The last ones (from what I can remember) do a lot of hands on dirty work to 'find success' in their website. (ooh, I like the sounds of THAT! "We help you to find the hidden success in your website"- 0.3cents per utterance ;-] )