iMac, 10.7.4, frequent spinning wheel

Model Name: iMac

Model Identifier: iMac10,1

Processor Name: Intel Core 2 Duo

Processor Speed: 3.06 GHz

Number of Processors: 1

Total Number of Cores: 2

L2 Cache: 3 MB

Memory: 4 GB

Bus Speed: 1.07 GHz

Boot ROM Version: IM101.00CC.B00

SMC Version (system): 1.53f13

Macintosh HD:

Capacity: 999.35 GB (999,345,127,424 bytes)

Available: 372.78 GB (372,778,373,120 bytes)

I get the spinning beach ball almost every time I do something; launch an app, quit an app, search for a file, save a file, switch between applications, emptying the trash, etc. You name it, it makes the ball spin. Sometimes for a minute or two, and sometimes it doesn't stop and I have to force quit an app or do a hard restart to get things back to normal.

I've booted from the install disc and have run disk utilities several times, verified, repaired, everything checked out OK. Still no change in behavior.

Very frustrating, it's almost unusable in this state.

Help!