The title says it all.
I played a long, brutal game with a great friend last night, and I almost had him beat early in the game. (I lost my focus on what I was doing though, and didn't take advantage of the opportunity when he was weak. My fault entirely.)
Once he began to build dreadnoughts, I found them almost impossible to kill. Once he upgraded them to lascannons, I was toast. Warbosses, nobz, tankbustas, slugga/shootas..even killa kans couldn't do it effectively. They killed so many models so quickly that I was unable to take them down fast enough to prevent him from reinforcing them with more. Not to mention their deepstrike ability, which really screws up a frontline defense.
Any tips on how to kill these *#$%@$ with Ork abilities?