Nope, I hate instant rematches for the title. If it is a controversial decision (Machida/Shogun 1) or a strange stoppage (Randy/Vitor 1) then sure. A close decision for an established great (if GSP had lost to Hendricks), then OK, but only for the GSPs and Silvas of the world.
Aside from that , the former champ should have to earn his rematch. Obviously he can have a short route to the belt, even just 1 match against a contender depending on the status of the division.
Immediate rematches should be a rare exception, not the norm. Champions are often only defending once or twice a year, you have to keep the division moving.