There is currently an 'issue' with promo codes, with perfectly valid promo codes showing as INVALID by the system (after much delay) I have contacted DreamHost regarding this issue and have yet to hear back from them. I can only suggest that you try again later, perhaps someone at DreamHost will fix the problem.
As for your other questions; I have been with DreamHost for a little while and for most of that time things have been excellent. However, recently there have been reports from users regarding slow loading times on their sites etc.
Personally, my sites are still working fine, but the Web admin panel is frequently slow or un-available, which does makes things extremely difficult.
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