On a totally unrelated note I didn't find anything interesting in my mailbox today either 
On a related note here's a thread I posted back in 2005 (I guess I've already placed all of these on our wiki Yair, so you'll find little new here)
I also have not found a duration fire spell that truly felt right. I dabbled with the idea of a MuIg(An) spell that turned a fire into a guard dog that would protect you as long as you kept feeding it wood to "eat".
Bargain spells don't actually have to be rituals, you can do plenty without sending your level over 50.
Until can be handled in a way that makes things very very cool. It can also be abused. It seems more like a rego vim spell than a duration and that "can not be dispelled" I suspect is a whole wasp's nest full of brokenness just waiting for the correct tactless player to kick it into swarming. But it is the same level as year and it's not that much harder to dispel. I'd allow an intellego vim spell to determine the condition to release the spell. Looking at the intellego vim guidelines on page 158 level 5 detects any active magic two magnitudes gives technique and form three magnitudes gives the casting magus's sigil (from HoH: True Lineages), I'd say that the condition for releasing a spell is about the same level of detail as the casting sigil. That means level 25 gets you a range touch spell that figures out how to lift the curse. That's probably a lower level than a perdo vim to dispell the effect.