Well, for arena (and more or less battlegrounds), you're pretty much stuck with a siphon life/soul link spec. It's the best spec for survivability, and can give some pretty okay damage through master demonologist bonuses. I don't know how well it stacks up against a sb spam, heavy afflic, or dest spec for pve damage though. Probably not bad.

+shadow &gt;= +spell &gt; stam &gt; resil/penetration/spell hit (depending on if you're doing pvp or pve). From what I've heard spell haste is a great dps boost for sb spam specs, but since I'm heavy afflic most of my damage is through dots, so I can't tell you firsthand. 

I can however tell you how to boost your dps in raids. Naturally, consumables are your friend. Bring shadow/spell damage pots, yummy +spell food and wizard oil (I can make the last 2 if you need, send me a mail in game and I'll let you know the mats). Just be sure to keep an eye on your threat. You'll do more damage overall if you save your soulshatter for boss fights, so don't go too nuts on trash. I usually throw up UA, my curse (usually shadow for trash, unless there are more mages than 'locks/spriests) and corr, then toss off SBs until the mob is low. If it's a multi pull, I'll start throwing dots up onto the next tanked target then, otherwise I'll either drain soul if I need the shard or hit shadowburn to squeeze in a little bit more dps before the mob dies. Rinse and repeat, and really keep a close eye on threat.

Boss fights are pretty similar, but with one small difference (assuming that it's a straightforward tank 'n spank). Put up all the dots you have, and keep 'em up. SB as much as you can in-between, but don't let the dots expire for more than a second or two if you can avoid it. Use soulshatter strategically. For example, on Prince I'll soulshatter at the beginning of phase 2, trinket up and burn as hard as I can without worrying about threat for a minute or so. 

Keep in mind that the number one way to keep your dps up is to NOT DIE. I've kicked myself so many bloody times for trying to squeeze in that extra little bit of dps, and winding up pulling aggro. Luckily, FSE tanks are great, and it's usually just me that dies, but then I drop from #2 or 3 on the list down to 5. And wind up putting a lot more stress on the other dps and healers, since the fight is that much longer.

Dethe-- believe it or not, but I don't have an unlimited mana pool. I just have 3 mana pools to manage that regen at different rates. Luckily, with dark pact my phase shifted imp keeps me well topped up most of the time. But (ask Jyggle for confirmation), I'll often run out of mana and imp mana during Illhoof, and have to lifetap (because I'm a nub and often forget to bring mana pots). It must be stressfull to keep me up when I'm getting pounded on by 5 imps and all of a sudden I lose 4k health. Sorry about that mang :)

Any specific questions?