As you may recall, Blizzard announced their intent to get rid of consumable ammo in Patch 3.1, only to withdraw the change a short time later, with the promise of reimplementing it at a nebulous later date. Now, it's been more or less assumed that said later date is Cataclysm itself, or at least Patch 4.0.
In a general forum post created to discuss ammo replacements, Ghostcrawler piped in to remind us that the only change announced for Cataclysm was the removal of ammo, with nothing else yet decided (or, more accurately, announced). While he did acknowledge the possibility of adding in new situational ammo, he did observe that the hassle of collecting and swapping different ammo types might grow old pretty quickly, especially for a class like the hunter that already needs to push a lot of buttons to play at peak potential, in addition to already having a pet to manage.
I do see some wisdom in Ghostcrawler's words. As someone who played a hunter relatively extensively during Burning Crusade and has recently begun leveling that hunter again via random dungeons, I can attest that we do have a lot to juggle if we want to put out a respectable level of DPS or PvP utility. One more thing to worry about could conceivably get a little bit tiresome.
That said, I'm a hybrid player at heart. I played a druid when I first started playing, and I play a death knight as my main now, and in both cases, I always keep a set of gear upgraded and ready for all their respective roles. Those sets include relics. I have my tanking relics and my DPS relics already. If ammo become a similar "relic" system, it might not be so bad. Being able to spice up your shooting with some procs from an ammo relic would be a great way to add a little bit of fun to the system without making it overwhelmingly unmanageable.
Of course, if they just take out ammo altogether and roll the extra DPS back into the base weapon damage, I wouldn't complain too much either. My engineer will be sort of sad that one more source of cash flow is gone, but then again, raw materials sometimes sell for more anyway.
World of Warcraft: Cataclysm will destroy Azeroth as we know it. Nothing will be the same. In WoW.com's Guide to Cataclysm you can find out everything you need to know about WoW's third expansion. From Goblins and Worgens to Mastery and Guild changes, it's all there for your cataclysmic enjoyment.