Locks are very fun. I created mine in TBC basically as a dot / fear bot due to my high ms back then. Haven't really touched my lock since then until a month ago or so when I brought him up to current times. At first I tried to do the old dot bot but it just really doesn't work. Then I took Demo for a spin which was great with the demonic leap but I found it's gameplay to be very annoying. After that I tried out Destruction and loved it. The Damage is really good, some nice big numbers. I found it to be really easy to get started on and it has a great 1-2-3 punch. It took me about a day to get the enchants sorted out / satchels but after about 2-3 wsgs I got the hang of destro very quickly.
Only issue for me is I'm still used to VW bubble and as a result my survivability is horrible. I die a lot on my lock. (guess that happens when you solo queue) More seasoned warlocks like Dorigon and Youredead do great though. Since Youredead is always running with the pack she usually finishes in the top 20% of damage and doesn't have an issue with deaths.
I'd say roll a lock and try destruction as it's probably the most viable. I don't play it enough to have a high survivability rate however, but I'll get there if I choose to play it more frequently. Your best bet is to queue with some heals or you'll find the issue of rogue (open---> run to heals) to be less frustrating than lock which can get blown up very quickly by several classes. As for what 5.4 will bring for locks it's anybody's game.
Either way make sure to post your findings in this thread if you do choose to check it out. There are others who would probably learn off of your observations!
Cheers buddy!
Mocha