I just got back onto WoW from a several month hiatus, and switched factions to boot. My very first character, a human paladin, is now my main, and was parked at level 47 from when I bugged out of alliance for horde.
First thing I noticed- I was absolutely horrible at leveling my professions. Horrible. I had chosen mining and blacksmithing, and they were at about 120. I did not, at the time, want to go about leveling them as I leveled, and went from 47-74 in about a week or so, not touching professions.
I realized I really did want to level my smithing, however, especially when I realized I could craft most of the gear I would need for heroics/Naxx. So I went into the task of leveling my professions and put questing on hold.
I mined every single ore I needed to level. I did hour long circuits in different areas and farmed every last ore, and sold the gear to guildies/players as needed, and made about a 1000 gold in the process. This guildie needed a set of plate after they reached 40? This one wanted some crafted adamantium blues? These enchanters rods sell for 40 gold a piece?
It was actually much more rewarding than leveling jewelcrafting, which I did for my horde pally. I could make full sets of gear and give it to my friends and have them use it, which I think was the original spirit of the profession building and leveling. But now, with mining leveling guides and profession level guides, I think much of that has changed. Questions like "Where do I find [ore]" are now replaced with links to these guides, and only the bare minimum of the recipes are used.
To top it all off, once I hit 80, most of the crafted gear will be easily replaced with gear from instances and heroics/badge gear. There will be no more need for my profession for myself after I get some of this gear- seemingly making it a waste of time.
Now, to be honest, some of the stat benefits to certain professions are meaningful, but are they meaningful enough to merit the time and possibly gold put into them in order to make them (semi) useful?