Well I figure I'll chime in here. I have RoadRunner, and on my Droid X both my accounts work flawlessly. However on my Galaxy Tab, only one of my accounts work, and the other I get a connection error, even though it passes the set up tests. So to experiment I made anew RoadRunner address and it works flawlessly like my other account.
I ended up just using K-9 Mail on the tablet instead of the native Android client which works flawlessly. I then did some reading on K-9 and found out its 100 percent based on Androids native client, but with MANY tweaks, options, additions, etc and is so much nicer.
I do know that Samsung uses their own email client on the Galaxy tablet, though I think it's just a skin (for tablet ease) over the native client.
Anyway, long story short... Road Runner's email is finicky.. While it works fine on one device, I had to use K-9 for the other.
I highly suggest K-9, very happy that a Verizon rep showed it to me.