Basically, the received wisdom as I understand it, is that a swap partition on flash memory is not generally advisable, as it involves lots of write operations which can wear out flash cells more quickly. (I also understand that apparently, modern flash memory and/or controllers have features which can mitigate this so it's less of a problem ("wear-levelling"?).)
Wear-levelling is a process where the controller keeps a constant count on how many times every cell has been written to, and tries to keep things so that all cells have equal writes to them. Commonly Flash-media like SD-cards and USB-sticks do not have wear-levelling and on such devices swap may wear out the device. On SSDs though you will always find wear-levelling, and on many kinds of internal Flash-technologies that are usually not available to the wider, general customer base.
On my Eee 701SD netbook (Arch Linux), to minimise wear on the SSD, I don't have a swap partition on the drive, and have moved the temp files and logging to a ramdisk (I can get away with this, having upgraded the machine's RAM to 2GB).
As said above, SSDs do have wear-levelling and as such having swap on an SSD isn't really a problem. Also, just the fact that there does exist a swap partition doesn't necessarily mean it's being used; your OS only uses it anyways if it seems to be running out of RAM, and if no such condition exists then there are no writes to the SSD.
However, I don't think this is an option on the RasPi, owing to its lower RAM (256MB on the Model B). Presumably it will need a swap partition, and this would need to be on the SD card. Does this mean I'll just have to assume that the card will wear out more quickly, and therefore be careful to back it up and reflash the contents onto a new card, when the old one "dies"?
The whole drive doesn't suddenly die if some cells die, meaning that you could e.g. buy a 16GB card, make a 14GB root partition for the OS, make a 1G swap partition at the 14GB->15GB mark and use that until it starts showing signs of corruption, then make a second swap partition at the 15GB-16GB mark and use that and so forth.
Also as I have used Flash media for all kinds of purposes for years now I would say that you could safely use it atleast for a year straight before you start getting issues. Atleast I have been able to use Flash media very heavily for a good, long time before it has started to show any kinds of symptoms, and with "very heavily" I do mean much more write-heavy tasks than simple swap.