So WHERE exactly is the best place to get my 4GBs of RAM? Crucial, OCW, NewEgg etc? Sorry, new at this...
Or is memory just memory?
Memory is just memory, though really cheap memory may have manufacturing defects and consistencies, so try to buy from a better brand (tons are listed in threads in these forums).
As stated above, memory removes the bottleneck that is your hard drive if you are running multiple programs. The more programs you run, the more memory you use. If it exceeds your RAM memory, then the operating system starts "swapping" data between your hard drive and RAM. RAM is MUUUCCCHHHH faster than reading data from a hard drive. So, the more RAM you have, the more can be stored in RAM, and the less often the operating system has to "swap" to the disk.
I use my MB for a number of tasks, and rarely shut the applications down (especially with spaces running). So, at any one time, I might be using Safari, Firefox, iMovie, iPhoto, iTunes and maybe another application (like WOrd or something) and can often run up to about 2.5GB RAM. So, the 4GB helps. You could also do 2.5 or 3GB, but for reasons that I wont' detail here, having matched memory sticks (i.e. 2GB+2GB instead of 1GB+2GB) helps boost performance of memory reads about 7%. So, if you figure you should at least buy one 2GB stick, then you are really talking about should you buy a second stick for $40 for a 7% memory performance boost and assurance that you want do any disk swaps (frequent memory swaps to disk also puts a strain on the harddrive over time).
I suppose $40 might be tight for some, but when installing in my $1500 laptop, I think it's a pretty good spend.
Just keep your original memory (and original HDD if you swap that out) so if you send in your laptop for service, you can pop in the original equipment before sending it.