Depends when the MBP update is. If it's after May, I can see Apple updating iMac with new CPUs in lower end (Clarkdale) and new GPUs but if the update is before it, I doubt it.
I think the spotlight will be on the Macbooks as they're overdue for an update, while the iMac has more recently been updated. Apple better put on a big show after all this waiting.
That's not even possible. 2.66GHz Arrandale is maybe little bit faster than 3.06GHz C2D but we won't see it in base MBP, likely high-end 15" and 17". Base MBP will get something like 2.13GHz or 2.26GHz which is way slower than 3.06GHz C2D.