Just finished up my nexus attempts for the night.

Omorok - piece of cake. I just leave my whole gorup on /follow, zoom camera out, and use left / right straffe passed to all toons when the spike pop. Just watch for spell reflection!
Anomalus - also easy. Nuke down the rifts when they spawn, I just drop consecreate for any of the little mobs that spawn out of the rifts and focus back on the boss. Groudning totems + chain heal helps.
Telestra - a real pain in the ass. I didn't get her yet, but I think i will next time with a few adjustments. The fire bombs are targetted AE, spread your team out a little before you engage. The rubber band is on a timer, I reccomend opening up with full dps / blow coodlowns etc ... if your dps is high enough you can get her to split (50%) before she rubber bands you. During rubber bands instant casts are the name of the game ... use shocks, riptide, ns + heals, heal pots .. when you land quickly regroup and heal up. I really think a small amount of resist gear would help here also .. with just frost aura I resist the ice blocks about half the time.
Keristraza - not tried yet of course.