By Paul Murphy, author of The Unix Guide to Defenestration
You see a lot of serious Unix people talking about reducing swap/paging space to a typical 512MB ragardless of what the real memory is. Don't apply that rule without careful thought: remember, even mirrored, the cost of swap only runs about $50/GB and there are lots of uses for a fast file system that go beyond simple swap or paging.
Keeping swap space small relative to real memory is usually good advice for a large machine with a well understood workload but terrible advice for a small machine running a mixed or unpredictable workload. For example, if you're responsible for a 6800 running Oracle in 96GB of RAM, your memory usage will be predictable down to the megabyte and you'll have no use for 192GB of parking space. If, on the other hand, you're supporting email users on a 250 with 2GB of installed RAM, having 4GB of available process parking will eventually make the difference between normal operation and a parade of users going in to see the boss - and closing the door behind them.
For swap, along with everything else, I generally prefer simple internal storage without software mediated mirroring, but there are two exceptions:
In all three cases, though, think carefully about workload and costs before committing to a configuration because, somewhere downstream, a few extra gigs of swap could save you from a stressful 3AM call in or a long struggle to maintain performance on an overloaded machine.