In general, you can expect any mounts that are 100% drop rates on difficult encounters to be changed instead to be rare drops on the boss instead; they don't like the idea of letting people simply get mounts for 'free' by defeating a boss. However, anything that requires farming -- like Protodrakes/achievement-based mounts -- is likely to stay.

This is all tentative and could change, but we don't really have a problem with protodrake farming. What we will probably do with really unusual mounts like Mimiron's Head and Invincible is make them a rare drop. The 100% drop rate won't make sense when you can overpower the content.

If you want to overpower the content for a drake though, go for it. Players who did it "legit" had the benefit of having the achievement and mount earlier than anyone else. The most prestigious mounts will change in Cataclysm.

Ghostcrawler on rare mounts

Titles are unlikely to be changed in any significant way: several of the 'heavy farming' achievements/titles (Loremaster, the Insane) have been announced to be unchanged, and you can expect that any titles which you currently have will stay. Since most titles are not based on luck, the only titles/achievements you can expect to see changed are the ones that are no longer possible, and will likely become Feats of Strength. In general, with limited changes to Northrend, this is more likely to be an issue for "old world" achievements than for Wrath of the Lich King titles and achievements.

There are likely a number of items dropped by rare creatures around the world that will be changing: in general, expect that any item that drops from a mob on Kalimdor or Eastern Kingdoms to have a chance to have disappeared completely. Some mobs definitely still exist, and they're trying to maintain 'interesting' mobs where the story allows it, but the state of the game is too early for us to know which of these drops are going to stick around.