It may be 'really solid' and doing great progression, but maybe that's not best for everyone. I know at 70 I had a lot more fun doing easy runs of Kara just for a good time, messing around with my friends and cracking jokes on vent, than I did of wiping all night in Hyjal (I was geared for ZA and did a fair amount of that too.) Not everyone is best served by awesome progression.

I'd recommend staying with the guild for a while too. Luckily Rogue is one of the more mathy classes, and often you can answer the question, 'what is the best gear for spec X', or 'what spec, with maxed gear, give me the best DPS'. If you want to hang with these guys you'll need to sharpen your game a bit. If that isn't for you, by all means thank them and look for another guild that is a bit less experienced, however you can learn a lot from them.

If you want to stay with them, I would recommend you first find out if there are any Rogues in the guild, or if anyone has an alt-Rogue that is geared, then go to all their armory pages and make note of their specs and stats. Be sure to note things like weapon speed, hit, crit, and attack power and look at the specs they have. If you have armory data 4 or 5 Rogues in full raiding gear (not PvP or questing, they will likely be different) try to look at their stats and specs and see how their gear works with their spec. Why would this person have a fast weapon that does less damage? Why would the other have a slower weapon? Why would one have more crit and another more haste? If you can't answer the questions, no problem, just be sure you know what you don't know.

Then do some background work. Read through the Elitist Jerks Rogue forums, and search for Vulajin and read what you can of his and try to find his new spreadsheet. You may also want to look up shadowpanther.net, there is a ton of information there.

Revisit your list of questions. See if you can answer some of them now. Then, take the questions you answered and the ones you aren't sure of and talk to the players that play the Rogues. Ask them if you can have some time to discuss Rogue stuff with them, and spend maybe half an hour or so going over things with them. Be sure to ask about attack rotations and how to increase raid utility. If you have a class lead for Rogue by all means pester the living crap out of them... that's their job... to help out the Rogues. :^)

There is a lot to playing a Rogue, but unlike many other classes, most of it actually has a definite answer because of the way Rogues work. It just takes some time to learn it all.