I never thought that I would ever need more than a gigabyte of RAM in my current PC. As it turned out, having more than a gigabyte of RAM can be quite beneficial in some, though not all circumstances.
If you're not much into computers, perhaps a beginner, or someone who rarely runs more than one program at a time, 256 MB of memory should be enough for you. If you're a power user who runs lots of apps simultaneously, 512 MB would be more to your liking. Actually 512 MB is the "sweet spot" for Windows XP. More than that, and you come to a point of diminishing returns, where additional memory would hardly yield any more performance.
Of course, that depends on what you actually do on your PC. Video and sound editing, and some newer games (like Battlefield 2) run faster if you have a gig of RAM. In fact Electronic Arts recommends a gig of RAM for this game, with 512 MB being the bare minimum.
Being somewhat addicted to Battlefield 2 lately (check out my Battlefield 2 post here), I realized that it can be quite a memory hog. Checking my task manager, I discovered that with even with only a few essential programs running in the background, running Battlefield 2 routinely occupies a memory footprint of approximately 1.34 gigabytes. As a result, I get annoying pauses every so often during gameplay lasting anywhere from two to fifteen seconds, whenever the program needs to load data from the hard disk. As anyone who plays first person shooters would know, even a split second delay could mean the difference between you fragging someone else or yourself getting fragged.
The solution, it turns out, is even more memory. I got another stick of 512 MB PC2700 DDR333 SDRAM for my (old) Athlon XP system, and it worked like a charm. Now the entire game fits within my physical system memory, negating the need to access virtual memory on disk. The annoying pauses finally disappeared. Don't think that the additional memory increases framerate, because it doesn't. What it does though, is basically load the entire game, along with all the graphics and textures into main memory, eliminating the distracting and irritating pauses associated with swapping data to and from hard disk during gameplay.
I guess I bought a little more time for my PC before the inevitable motherboard and CPU upgrade...perhaps a Socket 939 Athlon 64 system with 2 GB of RAM running the 64-bit edition of Windows XP Professional would be nice. :-)
What the inside of my PC looks like.
Note the third stick of RAM.