Until we see some beta units, it's all speculation. Primegrid was virtually made for GPUs as sieving and number crunching work very well with parallel processes. Combine this with other BOINC projects offering higher points per clock cycle than WCG and it's a very unfair comparison.

We just can't know how well any given science adapts to GPU until we see it running. Probably it will be faster than CPU (this isn't guaranteed for all applications) but the gain is anybody's guess.

Speaking of which, I do believe we were promised betas "early in 2012". Let me be the first to say then: It's the third already where are our beta units?

I'm hoping the hardware requirements will be modest in the same vein as the CPU client has been. My available GPUs don't have the RAM of the newer cards even though what I've got is enough to double the amount of BOINC credit I'm getting (with them running on Primegrid - I realize that may be a big caveat).
Of course whatever client drops when it comes will be more or less it, the project coders don't answer to me or my personal wishes nor should they. Just hoping is all.

I doubt that GPU memory will be an issue. Possibly shader count, but still unlikely. Saying as you didn't actually mention your GPU, all I can do is repeat myself and say that most NVidia GPU's are OpenCL1.0 capable, and most ATI/AMD HD 5000, 6000 and 7000 are also OpenCL capable. The HD 4000 series ATI/AMD cards have Beta-OpenCL support according to AMD. So the bigger cards are more likely to work and the lesser cards less likely. All GPU's that are OpenCL 1.0 capable will still need a recent driver. WCG has probably been running internal Beta tests, with scientists, techs and a few CA's chipping in. I'm sure they will advise when they are ready. Hope there is a bit more notice than, 'I will be submitting some Beta's later today'; so everyone can make sure they have the correct drivers. A Beta with random GPU drivers, spanning years, would be messy. Better to require a certain driver to participate.

PS. What about 'mid-year', just to limit 'early' to the first 4months

One thing alot of the gpu projects have done is limit cards to 256 meg of memory as an absolute minimum and some projects are requiring 1meg of memory on the cards, this is due to the need to fit ALL of the application on-board the gpu to take advantage of its speed. As stated ALL of this speculation will be answered after the first few Beta units are released.