Can I put this RAM into my iMac 27" mid 2010? (Corsair CMSO8GX3M2A1333C9)
Apple's memory upgrade page for your model iMac calls for PC-10600 SO-DIMMs.
http://support.apple.com/kb/ht4255

Those Corsair SO-DIMMs meet all the stated specifications, even though some sites erroneously list them as PC-10666 (Corsair lists them as PC-10600).

Furthermore, if you look through the reviews on Newegg and other sites for this memory, you can see reports of people using it successfully in their Macs.

So I would conclude that yes, it's safe to use it in your 2010 iMac.