Well I'll chime in that I've been having the same problem as the original poster and have been having it for several weeks now. I've opened several tickets and have communicated numerous times with Support.
First, they identified a saturated link to my database server which was supposedly fixed. My site worked great for a few days, then the sluggishness returned. After some back and forth, they decided to move me to a new server, but that didn't fix the problem. After some more back and forth, they recently (in the last couple of days) identified the problem as the network file server. That was supposedly fixed and my site worked well for a while today, but now has seemingly gone back to being slow again. Throughout all of this, I've also had sporadic email problems.
As you can imagine, I'm pretty exasperated by now, particularly since the problem is so erratic - sometimes my site works OK, other times it's slow, other times it's so slow as to the point of being unusable.