An additional 1GB is probably not going to be something obviously noticeable, unless you use programs which specifically benefit from that amount of memory. A Mac with 2GB has enough breathing room to perform basic tasks adequately, so more memory does not provide an exponential performance gain as far as those things go. For instance, I have 7GB in my Mac Pro, and having that much RAM doesn't benefit me at all for basic tasks, but when I want to record 12 tracks of digital audio at once, I can, which I couldn't with 2GB. This isn't the perfect analogy, but it's kind of like having 15 gallons of gas in your tank instead of 5, i.e. it's there if you need it and beneficial if you drive a distance or decide to go 120MPH, but if you are just going to the grocery store and back it's not going to be obvious.
If you started with, say, 512MB, and went to 2 or 3GB, there would be a very noticeable difference, and that is because 512MB is a small enough amount of RAM that the system is suffocating, so to speak. Adding more RAM therefore frees it up to breathe naturally. But you've already got enough memory that it was never really hurting in the first place.