I'm not entirely sold on leveling trade skills in World of Warcraft. By leveling up professions you can create armor, weapons, and goods that theoretically benefit your character. With a little luck, you can even make some money from your trade. It usually takes a major investment maximize your professions and get the goods that you want. In most cases I prefer to wait until I've reached the level cap to start professions.
There are two exceptions to this. Whenever I roll a character on a server that's new to me, I invest in skinning and mining and sell the materials for gold for my mount and equipment. I used to level fishing too. Until Blizzard added the aggressive mobs on the
The other exception was my Hunter. I leveled Engineering along with my character in order to make bullets. This was beneficial for gameplay, and I didn't feel like I was wasting gold for skill points. Aside from these two exceptions, I usually just wait until I'm level 70 and buy or farm materials for my chosen profession. I've even been known to switch professions when necessary.
I do also tend to level up First Aid, even on my healers. It's very helpful when out of mana. At this point I just skip Fishing and Cooking altogether.
What's your take on leveling professions?