After leveling my warlock as an Alchemist and Herbalist, I dropped Herbalism for Engineering shortly after I had completed the grind to High Warlord. I know, it was brilliant that I put effort into making all of those PvP trinkets AFTER I was done with PvP, but that's beside the point. So yeah, anyway, after the ridiculously expensive process of leveling engineering to 300, there I was, broke, an engineer with PvP trinkets that failed half the time (and sat unused in my bags the other half), and other items that no one else wanted or could use because they weren't foolish enough to pick up such a broken profession.
I thought about dropping engineering for a very long time, but never mustered the courage to drop it for fear that Bliz would decide to completely overhaul the profession the next day and actually make it worthwhile. There was a hoaxed list that was making the rounds on the WoW forums at the time, and while some of the items seemed nice ("Flying Machine" anyone?) but they just didn't have the wow-factor (no pun intended) that engineering desperately needed to keep me interested. I finally gave up hope and dropped the profession for herbalism, and I hoped to goodness that I wouldn't regret it. Now I hate myself for waiting so long.
With the alchemy and herbalism combo, I'm actively using my professions again and doing quite well with them. I discovered the recipe for Flask of Mighty Restoration shortly after dropping engineering, which has sold quite well. I also sell transmutations and/or their products regularly (xmute spec) and that results in a good chunk of change. So I went from making 0g per day from my professions to about 150-200g per day after dropping engineering. Lesson learned? I didn't drop it soon enough.
If any of you are still holding on to engineering, consider this. When April 1 came around, the Tin Foil Hat (a totally useless engineering item) joke appeared on the WoW website. Now, when Bliz directly makes fun of a profession, you know it HAS to be garbage. So, get to dropping it asap and move on to something else. You definitely won't regret it.