I have bitten my tongue as well for the last couple months, for I have always been a huge supporter of Dreamhost, and have referred them to many many clients. But these email issues have been a HUGE frustration for myself and all of my clients. If it would not be such a massive undertaking to move all domains, email accounts, mySQL db's, webdav directories, subdomains, etc. to another hosting provider, I would absolutely do it. I've had it.
Like other posters on this thread, I too would trade the gigantic storage options for rock-solid email servers. If Dreamhost is working on expanding and upgrading... and it affects their users negatively on almost a daily basis... then they should have communicated this better and devised a better way to do it. The current state of affairs is unacceptable.
As I write this, my email application is blowing up with constant "enter your password" screens. My clients are pissed off and want to know what is going on. It's literally bringing businesses to their knees.
If Dreamhost is truly building a more stable experience, my god... it better be watertight. If we put up with the last few months for an empty promise, I can assure you that your reputation will be tarnished and many of us out here will spread the word.