Ram_uses

It also makes your computer weigh more. Unless you have two 2gig sticks instead of three 1gig sticks, then it will make it weigh less.

As a general rule, more RAM is better unless your system or OS can't support it fully, or your programs are not using what you have now.
 

In terms of internet applications, the extra gig will give space on the ram for the browser to use if you are close to using 3 gig. Fairly useful for web browsing while playing a game that uses a lot of RAM.

If you are actually asking if its worth upgrading to 64-bit to make full use of 4 gig of RAM instead of being capped then you are probably better off with 32-bit since 64-bit uses more memory and will run 32-bit programs slightly slower, unless of course you are fully using that 3 gig and really need that little extra. If your currently doing a system install and plan to add more RAM later then definitely go with 64-bit so you don't need to reinstall later.