In my current campaign characters have the option to take CON loss instead of level loss 2 CON for raise dead, 1 CON for resurrection, 0 CON for true resurrection. This makes them gradually get weaker (but they can compensate through magic) without losing their effectiveness in all other areas. One PC has taken this option so far.
I also had a situation when a 6th level cleric attempted to use a raise dead scroll to recover a party member - it backfired and sucked levels from the cleric (i.e. gained negative levels) to give to the raisee. The cleric thought "hey, I didn't know it worked like *that*"
Cheers