I found an interesting thread that doesn't really relate to spreading swap out across multiple partitions but it discusses swap in general and also brings in another important term "thrashing". It's an interesting debate/argument (it's a large thread):
Swap vs No SwapIn a couple of the messages the term "thrashing" was brought up. I forgot about this important issue when it comes to swapping. Your RAM isn't only used for program code but also for caching program data and files. Less used code and data are paged out to your swap partition to make more room for caching (to increase performance). Generally it's good to have a fair amount of swap space so that the kernel can page out less used program data to make room in fast RAM for caching more utilized code/data.
Thrashing occurs if your swap partition is on the same drive as your "/" partition (or working partitions). Basically you want your swap space on a dedicated or low utilized drive. The reason for this is because you may be doing heavy I/O on your "/" partition that would trigger a lot of swap/paging activity. Well, when this happens your disk heads are going to be switching back and forth between your "/" partition and your swap partition very frequently. This can cause the system to come to a crawl (I would expect the farther apart the partitions are the slower the system would be).
So optimally you would want your swap on a low utilized disk (the disk heads can stay in pretty much the same spot). So m0r, you have your swap set up in a good way. It would be even better if you had several low utilized disks that you can spread the swap out over that would allow the kernel to stripe and increase performance even more. I would guess that in the case of only having two disks you would only want the swap on the least utilized disk as to prevent the thrashing scenerio.
