It's true that there have been posts in the forum about slow servers. But to put things in perspective: there are more than 120.000 domains hosted at Dreamhost, and they are not all complaining. I am one of those who don't complain. My personal experience is that DH is far better than any other host I've tried -- at no extra cost, considering all the features and disk space you get.
DH uses it's own control panel, and it's very different from the standard ones. But that's generally a good thing because it's custom made for DH. Some changes you make take effect within 5 minutes, others may take 2 hours or so. I have no experience with other panel systems, but cPanel is often mentioned here as comparison and the reply generally is that the DH panel is just good or better, it's just structured differently. So once you learn the way of the DH panel, you should be just as happy with it as with cPanel.
Squirrelmail is the only webmail system that is preinstalled from DH on your account, and as far as I know they are not planning to replace it. It's pretty okay (except that it uses frames with is always a curse). If you are server proficient, you could install any other webmail package for your account instead or as well as Squirrelmail.
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