Welcome to 70 where the rep is for grinding and the purples start getting sharded! Gratz!
At 70 the dividing line between PvP and PvE only gets wider as you progress in each respective area. What gear you should be going after is really dependent on which you're going after. If you love stun-locking clothies until they are nothing more than crying heaps of dissected flesh, go PvP. If you admire perfectly timed kicks and laughing at enrage timers with mocking joy, go raiding.
Many people keep two sets of gear, and correspondingly different talent tree specs for their toons for each environment. It's a bit of a pain, but worth it. You cannot excel at both PvE and PvP with the same gear/spec. You can "get by" and be mediocre, but you're not going to run BT as Shadow Step in Gladiator gear anymore than make over 1800 in 2v2 arenas with the t4 set and Combat Swords.
(*note: Before any of you start, I'm sure 1 or 2 counter-examples exist but let's not get side tracked with extremely rare oddities here.) For PvP you might start with
Theo's FAQ for a great ton of info on Arena rogues. The blue rep PvP items you mention (
Opportunist's Set) are an ok start for Battlegrounds so that you can begin to grind Honor, but not much else. And they are mediocre in PvE compared to....
....
The Assassination Set is where most of us PvE rogues get started. The 2-piece bonus is good and the pieces can carry you through Karazhan. Having to run and re-run instances for them also will help you learn good raiding/grouping habits, tactics, etc. For a solid start of the mechanics of the raiding rogue, start with
Elitist Jerks.
Of course these boards are full of info, just look through the many posts and you'll learn all sorts of things. My most important piece of advice is this: Don't just go by anyone's lists/suggestions/tips/whatever. Learn the basic mechanics of the class, get out there and actively improve as you get on with the getting on.
Good luck and here's to phat lootz!
Edited, Jul 7th 2008 12:48am by TherionSaysWhat