The stock HDD that came with my MacBook Pro was running a bit slow and consistently added a lot of heat inside the laptop, so I decided to switch it out for a 256 GB SSD from iFixit!
It went perfectly! I followed the guide on iFixit's website and didn't have any problems!
I was incredibly nervous about using SuperDuper, but it ended up being very simple and straightforward. Took about an hour to clone my HDD and transfer it to my new SSD using the external drive kit.
The drive replacement took about 30 minutes, mainly because I was nervous and kept having to wipe the sweat off my hands. Taking out the screws on the battery and HDD were the toughest part. Those suckers are small! But I used the tool kit that came with my new SSD and eventually got it done.
All in all, however, it went very smoothly and was nearly stress-free! I highly recommend using guides from iFixit.
The advice I would give to anybody wanting to try upgrading their computer hardware would be to just do it. I was almost going to spend $2,600 on a new MacBook Pro, but ended up doing my research and didn't even spend $400 on a solid state drive and brand up DDR3 RAM (admittedly got the RAM from Amazon...sorry iFixit team :P). My laptop runs better than it ever has and doesn't even come close to heating up as much as it did before I installed the upgrades.
Put simply: don't throw away a perfectly good laptop just because you want some new eye candy or because you don't think you're qualified to tweak your current system. It's a great learning experience and there's nothing more fulfilling than successfully booting up an old computer with brand new parts inside.