This example map shows a simple setup in Spirit to make a teleporter that chooses a destination from a set at random for each teleport.
As the weightings for each destination are set manually, you could use a similar setup to make, say, three destinations picked at random with another destination only chosen 1% of the time. The probabilities are endless!
This may be less effort though.
This also is a more true randomness as opposed to the... "simulated" randomness vanilla forces that setup to use. If used in a deathmatch map, people entering the teleporter at the same time might get stuck in each other. There's also the weighting thing, which would take serious redundancy to replicate in vanilla.
The setup I was considering when I tested this was a map where a certain section of the level could be cut off, and if that happens, have a teleporter that would effectively "respawn" the player back into the main part of the map.
Incidentally, does anyone know how the game picks a respawn point? Is it random, or on a cycle, or is it affected by where you die, etc.
EDIT: http://twhl.info/vault.php?map=6051