I don't use the announcement system, so I really can't comment on that. I'm also more of a 'hobbyist' than a serious e-business person, so the following may not be at all helpful, but I felt bad that no one else had responded.
I moved to Dreamhost primarily because of the wide range of features (I'm on the Code Warrior plan). I found DH oroginally because theonion.com hosts with them, and I figured anyone who'd host a site with that much class had to be worth a shot, even if they were a bit more expensive than some of the other companies around. I've now been hosting with them for about a year and a half, and don't plan on ever switching unless I someday setup my own server here for all my sites.
The first thing I noticed was the customer service aspect of DH. The announcements always have a sense of humour (usually they come from "The Happy [whatever] Team") and the staff seems to genuinely love what they're doing here. I've always been treated as a 'person' on the rare occassion I've had to make a support request (and usually it's just something dumb I've done like not chmoding the right folder or whatever ), and I have NEVER felt as though I was customer #283728723. That's very important to me.
I also appreciate that they're so on top of security issues. When the big PHP file upload vulnerability came out the other month, I received an e-mail in my box about DH's PHP having been updated even before I had a chance to read about the problem on several of the top "IT" news sites. I also appreciate that they don't turn things like Frontpage Extensions on by default, which could put my data at risk.
Finally, the wealth of features is great. I especially like the shell account, as I've been able to pick up a lot of Unix (my previous host did everything through "control panels"). Plus DH gives so many new languages and other toys to play with that by the time I've had a chance to play with all of them, I should have a pretty hefty CV if I ever start up a web development business of my own.
Anyway, that was long and rambly. Hope it helps maybe a little though.