Although it seems to be a little late for a reply to this thread, I just want to throw in: "YES! I'm a Dream Theater fan" ;-)
I saw them twice here in Germany. Absolute great concerts, but I think it is not possible to compare it with their concerts in the US or Canada. DT is not well-known here and they play concerts in front of 200 - 1000 persons. Quite familiar atmosphere ;-)

I just try to refresh my (former basic) knowledge of playing guitar, but John Petrucci is my big ideal.
It is quite old now but I think worth mentioning: John Petrucci's "Rock Discipline" is a very high-level guitar-lesson on DVD.