Macbook Pro - horrible performance - what can I do???

Question

Macbook Pro 15"
Late model 2010 (December)
2.66 GHz Intel Core i7
8GB 1067 MHz DDR3 RAM
500GB HDD (437GB/37GB Mac HDD/Bootcamp)
Hi,
When I got my MBP in Dec 2010, it was very snappy running Snow Leopard. 
My initial upgrade to Lion (Apple's version of MS Vista? LOL) had issues, I restored from Time Machine, but eventually got it installed.  Almost immediately, the performance drastically reduced.
Eventually, I took it into Apple, they re-installed Lion from scratch (wiped the hard disk), and I did a partial restore from Time Machine.  There's no guarantee I didn't regress some system files from my Time Machine backup.
The install of Mountain Lion was uneventful - the app store upgrade ran fine.
I was also getting a number of kernel panics, which were eventually isolated to (I think?) the GPU.  Apple replaced the GPU under the Apple Care warrantee.
So, ever since moving off the original operating system, my MBP has had horrid performance.  Some days worse than others, but lately very bad.
However, the timing could be a coincidence - I have also installed a number of third party tools (as we all do), and my HDD has 12GB out of 437GB left.  At times it has had < 1GB before I copied files to an external USB drive.  I don't deny my MBP could be bloated.
Sometimes when I close the laptop lid, then reopen it, the screen never recovers.  5 mins later the display is still black, and I have to cycle power.  Sometimes just tabbing to a new text input field within Safari can take 30 seconds to move to the next field.  Numerous other performance problems, I'm so sick of the spinning beach ball.
So, with that as background, some questions:
1) Any general advice on addressing poor performance under OS X 10.8.2?
2) Are there any *good quality* tools I can use to fix poor performance?  I installed Mackeeper 2012 for about 10 minutes, before further web research convinced me to uninstall immediately.  But I do like the concept, if a reputable company puts out a similar product.  What about Clean My Mac???
3) Are there any tools available to test my hardware?  I know Apple have them - that's how they detected the bad GPU.  I'd like to run a full diagnostic check of my hardware.
(However, I also booted into Boot Camp.  Windows 7 was very snappy, with the same hardware available to OS X.  I suspect my problem is software related.  Performance of the Boot Camp images under Parallels 8 is abysmal.  Yes, I know a VM adds overhead, but Windows used to be just fine under Parallels.)
4) Or should I just take it to the Genius Bar under my Apple Care coverage?  I've got 10 months left on the 3 year warrantee.
Any other advice more than welcome.  Right now, I'm close to just wiping the disk and installing Windows 7 ;-).  At this point, it really is unworkable, the performance is that bad.  I really *want* to like my Mac and OS X, but lately I think "It Just Works" is just a bunch of marketing hype ;-). 
Thanks,
Scott

Answer 1

Thanks for the quick reply...
1) Can I reinstall Mountain Lion from the recovery partition?  I know I could with Lion; I assume the app store upgrade to Mountain Lion updates the recovery partition?
2) How do I run a hardware diagnostics on my HDD?  Is there a utility that comes with Mountain Lion, or do I need to go to Apple?
3) Are there known apps that cause problems?  I totally agree with your advice above - I should have thought of it lol - but it will be a PITA to implement.  I can post a list of my apps if that will help.  Note that the poor performance occurs even when few apps are actually active, and happens shortly after a restart.
4)  How do I know what a TRUSTED app is?  For example, I've got Chrome, but I've heard it has ahem "issues" on the Mac.  But I don't know if that's the *cause* of the poor performance.
(Oops...ignore question #2, I'll search for how to do this...)
In short, if there is a way to shortcut these diagnostics, that would help.  But yeah, I can see that what you suggest will probably what I end up doing ;-/
Thanks again,
Scott