Orks are an interesting fleet. It really depends on what rule set you are using, and from there you will either do great or fail miserably. There are 4 "Official" rule sets.
1: Standard rules...Here the orks aren't terribly good. Fightabommaz are basically useless, so you have to rely on short range ineffective guns to do most of your damage (or torps...lots of torps). Spam out torps (shotgun them by AAF until in range where the turn you launch the torps is the turn they hit, so they can't be avoided and use the fightabommaz to clear any CAP), and hope that you can actually get into a boarding action.
2: 2007 FAQ rules...here the orks are decent, if I remember correctly. Fightabommaz can actually attack ships, and be useful.
3: 2010 FAQ rules...The invention of turret suppression made ork fleetz absurd. Fightabommaz are one of the best AC out there since they can always get some attacks in to even a battleship, and still double as fighters. Their guns still suck, but ork AC is OP in these rule sets, never actually lost a game with my orks with these rules.
4: Clan Rulez....This is an abomination of a document. The rules are poorly written and worded, and it's overall just a bad rule set.
If you have a group, I would check out the BFG:R ruleset, it's a much more comprehensive and balanced rule set (Our group just uses the fleet lists and standard rules...with our own modifications to the standard rules), and the orks do...ok. Torp shotgun in our ruleset isn't really a viable tactic, so they suffer.
Anyways, hope this helps!
