Ranked Commendations are currently purchasable for 30 Warzone Commendations (basically the same deal as Mercenary Commendations before patch 1.2), but in the future they should be the reward from Ranked Warzones. It's really only worth it right now to be buying them if you already have all the Battlemaster gear you need and don't have anything else to spend Warzone Commendations on.
After I got my level 40 set for myself and my main companion (actually bought him 2 sets so I could have a healer in the Marauder set), I basically started buying Ranked Commendations. Adrenals and Medpacks are certainly worthwhile, but hitting 50 with a large stockpile of commendations can help make the initial experience worth it.
Expertise is basically a way to balance damage/healing in PvP (along with the Trauma debuff that reduces healing). A decent explanation from over on the O-Boards:
If you had 12% Expertise before 1.2 your combat looked something like this when fighting someone with equal Expertise.
1000 Damage attack now hits for 1120 (12% damage increase)
1000 Damage attack has 134 points mitigated (12% damage reduction)
Over all the 1000 damage attack deals 986 damage.
And any healing is increased by 12%
The change has nothing to do with healing but completely to do with making PvE gear useless in PvP.
With the new stats your combat will look something like this when fighting someone with equal Expertise.
1000 Damage attack now hits for 1200 (20% damage increase)
1000 Damage attack has 200 points mitigated (16.5% damage reduction)
Overall the 1000 damage attack deals 1000 damage.
Any healing is increased by 12%
Damage mitigation and damage increase from expertise were just fixed to be completely in line with one another. Healers still get a bonus on top of that. That is just a fix. You will take more damage from DPS As will everyone but again that is simply a expertise fix.
Even if they made it
Damage increase 100%
Damage reduction 50%
Healing increase 12%
All that does is make it so you have to use expertise in PvP. Healing is untouched (assuming you are actually wearing pvp gear.)
Are you 50, Big D? As a fresh 50 in Recruit gear, I can do fine against equally-geared players but get tuned the @#%^ up against 50%-or-better Battlemaster gear. I'm having a hard time single-holding a node in tank spec, and get eaten alive while guarding a healer. I'm not complaining, I'm just saying that the PvP gear makes a huge difference post-50.
The PvP weapons you can get as you level have some expertise on them, but not enough to make a huge difference in Warzones.