How much RAM is recommended to run mountain lion?

Question

i have a 15in MBP (2008), 2.2 GHz Intel Core 2 Duo, 4 GB 667 MHz DDR2 SDRAM, OS 10.8.4, 791GB free space.
i'm getting a lot of beach balls, particularly in chrome and photoshop, forcing a lot of quitting/restarting. i see a lot of people at 8GB, but wanted to check first to make sure i'm not throwing money away. the economic reality of my life is that a new MBP will likely never happen.

Answer 1

I don't see a 2008 MBP with 2.2 Ghz, (only 2.4 Ghz or better) the Late 2007 meets your spec's of 2.2GHz, so perhaps you have a MacBook Pro 3,1 instead of a MacBook Pro 4,1.
The MacBook Pro 3,1 (Late 2007) was sold into Febuary 2008, so perhaps you didn't purchase what you expected.
You can find out, do a Apple menu > About This Mac > More information for a model identifier.
People recommend 4GB for the Lions, despite the 2GB Apple says it minimal needs.
However if your running bloatedware Chrome and Photoshop, you certainly could use more RAM.
The Late 2007 (3,1) it's possible to swtich out one of the 2GB's and put a 4GB module in, so you have 6GB total, same with the 4,1 and the Late 2008 (5,1) can hold 8GB. (2 x 4GB)
Until I know your model identifier I won't know for sure what to recommend.
Your problem isn't 100% RAM amount but it's slow speed, your older Intel Core 2 Duo + Mountain Lion bloatness + newer program bloatness.
It also could be you have been moving the computer around while the hard drive is spining, this causes the platters to become damaged and the sectors harder to read from which causes the beachballing to occur as well.
This can be fixed, but it will require you copying off all your data to a external storage drive (do not use TimeMachine or clones to restore here), the booting into RecoveryHD and using Disk Utiltiy to 3x overwrite erase your MacintoshHD parttition (takes a long time to finish) then reinstalling OS X, your programs from original sources and then finally your files from backup.
Reset your Mac
If you had any software issues, those obviously would be resolved also, unless you installed programs that were not ideal or compatible, like third party anti-virus (unneded) or the trashware called Mackeeper (avoid!)
If you go this route, take your time installing software until you see a performance issue, then that's likely a problem.
Chrome is bloatware attempting to use the browser to do everything, spawning a zillion seperate processes for each tab and eating memory like candy, avoid it and use the much faster Firefox instead.
Photoshop you can't help, but what you can do is allow it to have as much RAM as possible by not running other programs at the same time. The ability of the Lions to restart programs/windows from the last session should be avoided.
Why is my computer slow?
https://discussions.apple.com/community/notebooks/macbook_pro?view=documents#/