a good friend of mine has a build thats almost identical to the destro one linked above. the only difference is life tap is swapped for (yes, thats right) pyroclasm. he knows that, technically, improved life tap would be better, but he gets a kick out of soul fire critting people for OMGWTFMYFACE and then watching them keel over a half second later, stunned, with an expression of utter pain on their faces.
destro can be quite viable in pvp, and youll completely tear certain classes to pieces without even really trying. nether protection can be so unbelievably hax at times its not even funny. shadow priests, fire mages and pretty much all locks are easy prey for you. theyll all proc nether protection quite often, giving you complete immunity to their main school of damage for a few seconds, which is ample time to completely pwn them. other destro locks that are smart can be a challenge, but its definetely intense as you see who has the faster reaction times.
melee can be a problem, even if you use a succubus (and you should) because most melee can kill a succy pretty quickly. but even then if you can get a few incinerates or shadow bolts off you can usually bring them down before they kill you. shadowfury offers great pvp CC, and the combination of a few seeds + shadowfury + howl of terror can sow discord amongst the enemy ranks like nothing else.
the major weakness of destro, from what ive seen, is its somewhat group dependent. you need to find either a healer to keep your *** alive, or some other class to run interference for you while you kill stuff (healers can double as lifegiver and interferer, but having a third class interfere is generally easier on your healer). my friend and i will go into bg's with a priest buddy (war/disc priest/destro lock) and have a ball.
for lawls, grab zerking, have one friend distract an opponent, hit all your trinkets, and soul fire your friends target. back before they changed PI into what it is now, my friend was able to get some monstrous soul fire crits, on the order of 7k+ on high-resilience targets with zerking and PI up. he once procced cheat death on a rogue at 68%. im sitting there hitting this rogue, wondering why i all of a sudden started critting for 18 instead of 1800, and my friend goes "oh, damn, sorry man, i procced cheat death". needless to say, that rogue was surprised when i executed him moments later and (gasp!) cheat death didnt go off.
destro is great fun in pvp, but it needs support so shine. thankfully, with this destro pvp build you can put out respectable damage in a raid. not as much as the 021/40 shadow destro lock can, but still pretty good. whether its good enough to justify a raid spot i cant say, but if youre raiders are all big on min/maxing then chances are theyd want you to be 0/21/40. you can still pvp as 0/21/40, you just lack shadowfury as a defense or crowd control mechanism. all that means is you require more support to do your thang and youre a little less dangerous to large groups of people.