Model Imac 27" mid 2011. 2.7 GHz processer Intel core i5. Memory 4GB. Memory using Bank 0/dimmo--2GB DDR3, 1333 mhz status ok. Bank 1 same. Bank 0/dimmi - empty Bank 1/Dimmi Empty. MacIntosh HD: Avail 921.86 GB Capicity: 998.97GB. Flash player using 7.4MB.
Couple of thoughts - 10.10.2 is available - you might consider installing that and see if it helps. The other thought I had - was yosemite a fresh install or an upgrade over your last version of OS X? Some have had issues with upgrading.
The other thought is a dying hard drive but it may be too soon to say that.
Lisa is confused. She is apparently part of the public beta test program, and got the 10.10.2 betas (the second one came out just yesterday).
10.10.2 hasn't been released yet, and has nothing to do with fixing this issue. The OP kindly let us know that free space wasn't the issue, so that leaves the options of un-updated Flash, too many apps left open ("close" not the same as "quit") eating up all the RAM, or a failing hard drive.
Yosemite 10.10.2 is still in beta. If you were part of the public Yosemite beta testing, then you likely have a pre-release version installed. In fact, a new beta was just pushed out this week so I am guessing the final 10.10.2 will be released soon. But I doubt your problem is software or OS version related. It is your hardware.
If you are using either Mavericks or Yosemite, 4 GB RAM is not enough. I had a similar problem with incredible slowness on a 2012 MBP and going from 4 GB to 8GB made a tremendous difference. Upgrade more if you can. I also then installed a SSD and my MBP became lightening fast. If you have some money hanging around, add some RAM and see what happens.