Similar to the exploits possible with modern warfare 2's "tactical insertion" care would need to be taken to avoid players dropping "their" spawn point or whatever in the middle of your base.
Also /sethome in the SMP commands has aspects f this to a certain extent. However, it would be nice to have some kind of "spawn block" you can put in single player. Then, you can sleep in a bed while exploring, but know you will revive in another set location if you die. However, that could be used as a cheap mans teleporter, make it an EU expense to use?
I don't think this would be the case.
I can already sleep in a bed to set my spawn, so why use a spawn block instead?
Also, you COULD just destroy the spawn block to keep someone from spawning.