I'm using Zen Cart, and it's actually not that bad... (gnastiest stuff was pretty much Godaddy's fault). And the learning curve is actually not that bad either. And if you don't have my phone number, I can PM you...
This latest screw up was my fault - I left something where I shouldn't have... Eventually figured it out, and fixed it. More learning curve.
I'm using Linkpoint for the credit card stuff, and Derek goes through Comodo for their SSL stuff...