At the price of it these day's, why not just chuck in some more. You'll probably notice a little difference, but don't think doubling your RAM will double the speed. There's a lot more variables to consider even down to badly written software (I do this, not the bad sofwtare, mines always super sleek

. You'll probably need more memeory eventually anyway. Software development has become so 'lazy' these days as developers don't have to think about proper space saving, they just rely on people to up the processor speed and memory power.
Look at XP and the amount of memory you need for it compared to 95 say. Doesn't run at 100 times the speed does it? OK, there's a bit more to XP, but a lot of it is just forced technology that we don't actually need IMO. What extra facilities in XP could you not live without (as an average user)?? People think the application is a lot more complicated, not really, it's just written badly and eats power.
PS. Games are completely different kettle of fish as they are constantly having to compute algorithms (hugely resource hungry) and the likes and their requirements shouldn't be likened to applications software - even large apps. I used to write game engines.
So put in some more memory, but remember, it's a viscious cricle between developers and hardware (money grabbing which suits both) and your machine will always run a little slower than you would like........ gets my goat up every time my machine starts connecting to some Microsoft crap.......I only want to type a quick letter.......
Agree with CkB.