Commerce Server just saved me months of work
I was scheduled to do a project involving replacing Site Server with Commerce Server. Fortunately for me, we had so many problems with permissions all over and Microsoft Support was unable to help us and there was so little support available on the web ... so the project got canned.
I lost about a month of time that I spent researching and trying to just get the sample site that microsoft offers working, but I've been saved from another 3-4 months of the hell that is using MS server products (I had a ton of trouble with Sharepoint due to the fact that the documention included with SPS2003 was actually just for WSS, so it was just a waste of disk space. The only support available was a bunch of Belgian and German bloggers who were also trying to struggle through the process of using SPS with no real support). Since I'm salaried and have a proven track record of delivering projects on time, relatively bug-free, and within budget, I, personally, have nothing to worry about. Also our company has good relationships with our clients so we have nothing to worry about. Our client is a multibillion dollar company so they've got nothing to worry about, except that their technology audits are getting increasingly critical of the fact that their site still uses Site Server for some functionality.
Commerce Server looked pretty cool on paper and has some features that I think would have been incredibly useful to our client, but whatever. I think this call will be reviewed in a few months, so we'll see what comes of it.