Parallel limbs have a less acute angle from the riser, and when the bow is release rather than having recoil back towardsthe shooter, the recoil of the limbs is directed back into the riser essentially at itself, thus significantly reducing handshock. The feel of shooting a parallel limb vs. a curved limb bow is phenomonally different in a good way in my opinion, but you will still find a lot of TARGET archers shooting curved limb bows for the LONG axle-to-axle from my understanding.
Best example, is looking at the Hoyt website(
http://www.hoyt.com/compound_bows/)with all the bows side by side, the Powerhawk, Alphamax, and Katera bows are all "parallel limb" while the Ultra Elite, Pro Elite and Montega are all "curved-limb" bows.