I suppose we could view this as a good thing: we're not being f-ed with. There is no need to change a whole lot as far as guides and such go. It's going to killing as usual for 'locks in 4.2, with few notable exceptions.
Here's the big one:
Glyph of Soul Swap now applies a 30-second cooldown to Soul Swap, up from 15 seconds.Holy fel! Double? Really? Was it that OP? Well, that sucks. It already feels like years before the damned thing is off cooldown. So much for having a cool, useful spell to make us not suck on trash. I guess I'll go back to living for boss-meters now. It may be worth dropping that glyph for something else now. Not sure what. I'm going to have to look into it I think. You're basically only going to want to use it to preserve dots from one target to the next, and you probably will only be able to do that once. Count me in for AoE on trash pulls because that's the only way I'm going to be helpful.
Otherwise, there's some bug fix (regarding leaving combat while channeling Drain Soul), Soul Fire is now available earlier (level 20), and Soul Harvest has a new spell effect. That effect better be f-in awesome. Like, purple lighting should shoot from my fingertips and burn holes in nearby Mage robes.
For Warlocks, this is a pretty boring patch. I don't particularly like the major change (can you tell), but it's tolerable. It's doesn't really effect most bosses and it basically just puts us solidly back in the "stays on boss" class brigade. No more helping with the adds or anything useful like that. I guess it's a PvP balance thing, so whatever.
Good news is that there's a lot of gear (and some new dailies) opening up. Saga's got a great little list going rounding up the new stuff. Check it out if you're looking for something to make you smile. Gear sometimes has that effect, especially when patch notes fail.