Yes, the "page out" number is cumulative, but "swap used" is not. It's a measure of how much has been paged to disk and is still there right now. Again, anything greater than zero means you don't have enough RAM. Whether you should rush out and buy more is a different story, and there is no clear answer to that question because it ultimately comes down to one question: can you afford more. If the answer is yes, then it doesn't really matter what the numbers look like. Just get more RAM and be done with it. If "swap used" is 3GB, you need at least that much more RAM.
You can watch the system paging to disk at the command line using "vm_stat". For example, "vm_stat 15" spits out a line every fifteen seconds showing memory usage. These numbers are in pages, and one page is 4kB.
Really, if you're seeing beachballs and there are signs you don't have enough RAM, then you really should be getting more RAM. If you have a lot of programs open but almost never switch between them, then paging out and paging in is a little like saving your documents, closing the program, and then reopening, but it happens in the background.
There's the question of whether you don't have enough RAM, and that's very simple to answer. If pageouts is greater than zero, you don't have enough RAM. The other question of whether you should buy more is not so simple. If pageouts is greater than zero, and you can easily afford more, then buy more. Your system will put it to good use. You can never have too much RAM. If you can't easily afford more RAM, well... you'll just have to figure out if it's worth it to yourself.