If you checked the most recent Patch 3.3 PTR patch notes, a comparison of spells would show that Blizzard has reduced a lot of spells' cooldowns by a notable amount. This makes a significant impact on the playing environment on numerous levels, as most of these spells on long cooldowns were long considered to be powerful abilities whose use were once thought situational.
These shorter cooldowns will see more abilities in play, figuring more into dungeons, questing, or world PvP. Most of these abilities still won't see action in Arenas, where the allowable spells have been limited to abilities with cooldowns below ten minutes (down from fifteen). The change appears to be a direct result of many spell cooldowns being reduced.
This continues a trend in shortened cooldowns, reflecting what Ghostcrawler said in one thread about how Blizzard "in general (has) been moving away from long cooldowns, anyway." Players saw this when the iconic long-cooldown ability Lay on Hands -- an inevitable Patch 3.3 candidate for a nerf -- became usable every 20 minutes from a formerly mind-numbing one hour. More abilities are now being adjusted to be usable more often and, when necessary, balanced accordingly. Check out the full list after the jump.