For a general use case more is always better. If you have an expectation to use it for more than a year or two, more is always better. Even if you really really plan on doing one very specific and defined thing with it, more is almost always better. Recall the quote about 640K being more than enough (which Gates may or may not have said, he now claims he did not) and how well that turned out. The other aspect to consider, unless you have a truly nailed down specific use case, you will likely do more and more as things occur to you.
Given the cost differential between 1Gb and 4Gb, buy the 4 Gb model. It is not going to do anything worse, other than use a tiny bit more power and it will be much more future proof. This equation obviously changes for large scale deployments but for the home user the differential we are talking about is roughly the price of a large pizza. The differential as a percentage drops even further if you are actually buying all the bits of gear you need to deploy a full desktop (monitor, power supply, cables, mouse, keyboard). Buy the 4 Gb model.