RAM question

Hi all,
I got my first mac last week! It's the 2ghz macbook pro. After playing around learning new things about the operating system, i found a widget called iStat nano - which shows me cpu, hard disk, ram usage etc.

What i noticed about the ram is that even though I didn't have any programs open and only a few widgets active, that the ram usage was maxed out with about 64mb left!

I'm just wondering what the benefits would be of buying a 1gb ram chip for my mac? On a pc obviously it makes your machine 'run faster' but since this is a completely different operating system which would no doubt use about a 1gb swap file on a 7200rpm hard drive - just how much of a difference would it make?

Lastly, on safari (and firefox) i'm noticing that whenever CSS Opacity is used on tables, that they slow down dramatically... when you try to scroll down a page, its very choppy...

here's some example code:

table {
width: 50%;
margin-right: %;
margin-left: %;
filterlpha(opacity=50);
opacity: 0.5;
-moz-opacity:0.5;
}

thanks in advance.