SSD causes freezes and beach balls
This may also be an issue with the ICH8-M AHCI SATA interface chip. I have a late 2008 MBP that came with a 250 GB HD. I upgraded to a 640 GB and had endless beach balls. Turns out the models with a ICH8-M AHCI and a PATA superdrive interface cannot be upgraded higher than a 320 GB 7200rpm HD. Anything faster or larger will stall out as the FW for the ICH8-M AHCI cannot be upgraded beyond SATA I speed without killing the PATA interface.
Some models with a ICH8-M AHCI and a SATA superdrive interface can be upgraded with a FW update released by Apple.
Check for updates.