This really paid off later when I was able to harvest much of my own black dragonscale for the mount quest. On my hunter, who I skilled up to 300 in dragonscale leatherworking, it was a similar idea, but backwards. I'd send in my pet, skin the last mob, and then work on killing the next. This gave my pet a little bit more time to build threat, and made it very unlikely that I'd pull the mob back onto myself. On the priest it's a similar situation to the Warlock, since I have the Spirit Tap skill, which increases my spirit after I kill something, it's best for me to wait 3-4 seconds between mobs anyway to regen to full mana. Skinning fills that gap nicely.
On the warrior, I had two problems. First, I wanted to skill up Blacksmithing, and the obvious skill to go with blacksmithing is mining. The issue is that there are, on the basis of server population anyway, very few mining nodes. Consider that skinners basically create their own nodes, and the nodes respawn as fast as the mobs respawn. Mining nodes take, comparatively, a very long time to respawn. On a server with a very high population, I end up having to compete with a lot of other miners, who were all after the same limited resource. Second, for a warrior downtime between fights is very bad. If you miss hitting Execute to kill the mob, and with a big 2 handed weapon that's pretty frequent, you'll end the fight with a big pile of rage built up. The best thing to do is bandage up quickly and find the next target. Mining really distracts from the flow of a warrior, and skinning would be much worse.
I found when skilling up blacksmithing it was far easier to farm cash and buy materials than to mine them myself. Which I always thought was cheating somehow.
Oddly enough, given the server population I had very few issues with skilling up herbalism on my druid. The ability to stealth up to a flower and pick it while avoiding the mobs around the flower made it a lot easier. I know there's a lot of competition for Dreamfoil since it's used by nearly everything you'd want at level 60 (major mana potions, fire protection potions) but you can still skill up on Icecap and other high-value herbs without nearly as many problems.
I think that skilling up skinning was very easy. I never really even tried to hit 300, it just happened. Skilling up herbalism was easy, but was made even easier by playing a class that can stealth past mobs. Skilling up mining is frustrating and difficult. Much of my difficulty with mining, however, is because of high server population though. I think I'd have a lot fewer problems on a lower population server.
Thoughts? What gathering professions do you have? How are they working with the flow of your playstyle? Are they profitable, are you using them to skill up a crafting profession, and are you getting what you need for crafting?