Barb,
Just like Chris I have only worked with a few CMS systems outside of DNN, one of which was a CMS system by a company called CrownPeak, I didn't deal directly with them, but I know how much of a pain it ended up being, granted they are "ok" now, but the uptake was not only much longer than necessary but the support was incredibly lacking and the costs far exceeded the budget.
I have to say that I agree for the most part with the list that MMerrick posted above, I think that does a fairly good job of capturing the pros and cons. I would like to elaborate a bit on the products listing just given MY experiences with actual CMS products (Numbered to match his numbers...)
3.) I cannot stress how big of a deal this could be, with most CMS solutions that I have noticed if they are providing the service in one way or another they are responsible for the data that hosts your site, if they have cut corners on backups, hardware, or any of the like you could be greatly effected.
4.) This is SO true of commerical products, sometimes they are so up on getting the "flashy" marketing pieces in there that major basic bugs sit for a long time
8.) This one is the biggest of all, 99.9% of the time you will NOT be able to customize their solution without paying them to do so. Their upgrades/customizations are typically VERY costly ($140-250/hr) from what i have experienced when talking with providers. Depending on your business processes, this could be a HUGE killer.
Again, this is just from my exposure with CMS solutions in general.
As Chris mentioned above since you are posting here on DNN for the most part you are only going to be getting responses from some of the "more seasoned" individuals, those of us that are activly using DNN and are activly contributing to the community as we are ones that constantly monitor the forums here on the DNN site. Many others might have input however discussion topics like this at times can get buried by the sheer amount of traffic that this forum gets. I hope that some of this can help you make a decision.