Just my two pennies: I'm currently leveling up my lock to mainly PvP (BGs and Arena 2s) with some easy raiding/heroics on the side (Kara, Gruuls, Mags) until I fully spec for Arena. Here's my basic plan of gear upgrade:
Stop at 69 and grind marks for AB, EotS, and WSG until I have enough. For full PvP honor gear (Merc. Glad. + full Vin) it's something like 90 marks each for everything except WSG and it's just easier to do these at 69. At 70 I'll grind most of the AV marks and honor as AV has higher honor per hour in my battlegroup. With any luck I'll have tons of honor going into 70, though probably not capped. At the same time (i.e. 69) I'll be finishing up my FSW set for raiding. Be sure to have at least a few good pieces for PvE to switch to! For non-tailors I'd suggest at least a couple pieces of the Oblivion stuff.
With any luck I'll have close to enough honor at 70 for the Spellblade/Off-hand, Vindicators rings/belt/boots and some left over to work on the new Guardian neck. Add these to the rep PvP blues and I'll be well-set for BGs and maybe a few introductory arena matches. Switch out the FSW stuff and I'm ready to make Prince my personal foot stool. At least in theory.
For spec: I plan on keeping to deep affliction at 69-70 until I finish off the honor-purchasable gear and get serious about arena (then switching to Sl/Sl). UA (or even 40/x/11) builds do reasonably well in early raiding and BGs but hey are a bit squishy in arenas though, so be forewarned. There are trade-offs of course: iHoT or Malediction, CoEx or iCoA, etc. But those I leave to your better judgment and to those better at theorycraft than I am. There is also a case to be made for Demo builds for BGs and Kara (7/41/11 ish) but from what I've seen the total damage is slightly better in t4 content as UA and the instant casts are nice for PvP. Again it's a worthy debate, up to you.
I'm sure there's probably a better or more efficient way to do it, but that's the best I've come up with. Good luck and here's to phat lootz!