AbleCommerce 7 is a lot simpler in its architecture than the previous version meaning a lot less pain for developers. Its weakness, however, is its general web site page content management, which is a strength of SF.
We have not yet done extensive research into it's E-commerce provider either but we plan to do so this year as AbleCommerce and Sitefinity are now our two flagship products.
As far as integration between the two systems goes, I guess you need to ask yourself how far do you want to go. These are both enterprise-level applications and to fully integrate them into one system maybe a bit of a challenge. Perhaps a system whereby all content and product data is managed by SF but all order management is handled by AC could work. Or maybe a synchronisation tool between the two systems.
Currently we deploy them as two separate systems. One thing is for sure, there is great demand, at least in our market, for an integrated "killer" CMS/e-commerce application bringing the best of SF and AC together.
I really encourage more discussion on this from the SF/AC community. It would be great to hear other's thoughts.