hooo so many false ideas and bad specs in here...
the best specs for warlock dps pre TBC are:
30/0/21 (ruin, +10%shadow dam, bane, imp shadow bolt)
7/21/21 +2 (demon sac, bane imp shadow bolt, ruin)
0/30/21 (imp out, bane, imp shadow bolt, bane)
other spec are just not as good.
bane makes your shadow bolt deal 20%more damage.
ruin increases your total damage by 1%for each1%crit you have.
imp shadow bolt = +20%damage after a crit bolt (dot do not consume the buff but are affected by it)
7/21/21+2 is the highest possible damage but it means no pet, which is kind of bad in my opinion.
30/0/21 is my favorite, you loose 5%shadow dam for useless talents and imp buff.
0/30/21 is for when you have lots of +dam, the imp is your super hero as he decreases your threat by 20% (only way for a warlock to reduce his aggro).
PvP builds are totally differents with main focus on either heacy destruction (conflag) / soul link / curse of exhaustion.
after TBC is another story.