I have extra sets for all my bows.  3 for my BW, 2 for my Robertson (soon to be 3), 3 for my Schafer, etc, etc...

I love switching back and forth.  It's like a new bow each time:)

Getting a second set of limbs for my Morrison ILF. Definately the beauty of the system is trying different builders limbs.

Uh, last time I counted I had 10 sets of Black Widow limbs for 2 risers.  Never changed much either except for special cases - summer target or getting in shape for my buffalo or moose hunt.  Just picked them up used at the right price here and there.  

If you ever plan to travel and hunt it is worth it to pack along an extra set of limbs.  You could break a limb accidentally - say drop your bow out of a tree or something - you'll likely never break a riser unless something catastrophic happens - then you will probably have bigger problems than a broken bow.

Ryan

I have two sets for my Blacktail.  Plan on keeping the bow for a long time and figured one day I won't be able to shoot the set I'm using now.  Did shoot the other set most of last summer as I was working on form but also have a 40lb bow which if better for practicing my form so went back to the heavier limbs all the time now.

The only bow I have extra limbs for are my Bear TDs. I have a few risers and 4 sets of limbs.

I should probably buy a pair of extra limbs for my Silvertip that are 5-6 pounds lighter but I don't think I'd shoot them unless I physically couldn't handle my hunting limbs.