My own campaign is quite a "multisystem" one... We started using the standard OGL Conan rules but they suck so much that we all decided to change the system to a variant of the Chaosium Elric rules (some of my conversions notes can be found on the Conan forum). Still not being satisfied, I then moved to MRQ for a while. Both system are quite good but there are still things not to my taste in both, so perhaps I'll try to merge them, taking the best of both worlds (Even some ideas from the OGL could be included).
In my eternal quest to find the perfect Conan system, I unearthed the old Conan RPG from TSR (I made an old campaign in 85 using this rules). Although the game has an "unfinished" flavor (like many of the TSR games published at that time), I still find the rules really interesting and the game really run smoothly. So my next adventure will be using this rules but I still don't know if I will keep them or go back to the D100 system... I'll probably have a look at the new Elric rules before making another change...