the iMac 27" WILL accept 32GB of RAM.
i just dropped in the 32GB set from Crucial. literally took 2 minutes. machine recognizes the change in "About this MAC."
To be clear, concise & factual:
The 27" iMacs from Mid 2010 i5 processor & up will accept 32Gb of Ram.
The 27" i3 processor WILL NOT. 16Gb max in that machine.