Leather working - that's gone pretty static for my main - its not worth the cost to buy/make the IC rep patterns for me and I really don't have anything that's high demand on the AH - all I do now is make the occasional leg patch for myself or friends when they upgrade. However, the profession served me well for leveling and gave me a couple of nice 200 level items to start myself with at level 80 (this was when the xpac first came out, thus giving me a big edge tanking heroics when I dinged) so I give LW thumbs up for leveling but thumbs down for maintaining.
JC - a good consistent profession as the cuts help all my toons with leveling and gear upgrades. I'm sure I could make some nice cash playing the AH with my gems but I've got too many alts who are constantly upgrading gear to spare any so thumbs up for both leveling and maintaining.
Alchemy - like JC - my alchy alt stays busy making flasks and since all my toons do the fishing dailies I've got a steady supply of pygmy oil to make into Guru elixirs for AH bait. The xmutes are invaluable for making metas or simply convertering earth to useful elements, being able to turn "trash" gems into the 10k pvp honor gems is priceless and saronite to titanium isn't half bad either, plus, every three days I do my research for a shot at free flasks - definitely thumbs up for leveling and maintaining.
Tailoring - haven't made any new gear in a while, so it's on par with LW in that the patches are the only upgrades it makes, however, there's the bags - as a packrat the 20 and 22 slot bags are priceless to me, plus, I make some nice cash turning netherweave cloth into AH bait so thumb up for leveling and maintenance.
Enchanting - same as JC - it's a miracle I'm able to keep any chanting mats in stock - if I spent a weekend doing nothing but randoms on my chanter toon then I'd probably make a grand or two selling the disenchanted mats on the AH - two thumbs up again.
Engineering - was beautiful for leveling having all those wonderful toys to give my toon an edge when it's gear sucked (leveled as a ret pally - engineering is a must for that class spec IMO) and of course the goggles were wonderful when the toon could finally wear them - better then any 200 level gear out there. Sadly, the skill's post leveling use is minimal - the occasional scope and ammo for my hunter is nice and Jeeves and Molly are nothing to sneeze at if I get a group that's willing to chain run randoms but I open up my engineering window so rarely I swear there's a puff of dust and cobwebs when I do. So thumbs up for leveling but thumbs down for maintenance.
Inscription - except for the shoulder chants the rest of it is fairly useless when leveling. Occasionally I'll have a use for the hearth scrolls but that might be once a month. The cards are basically one shot wonders and the rewards from them barely last long enough to justify the cost. The darkmoon cards are questionable as the cost to make seems to exceed the cost of just buying them outright - really about the only use for leveling are the shoulder buffs (extremely nice though) and the scrolls that can replicate the priest STA buff (but not till you hit 80). Yes, you get all the scrolls you can eat but now that they've nerfed stacking them with each other and many other buffs the benefit of scrolls is minimal. Maintenance is slightly better as, assuming your inscriptionist leveled first and has everything, you can hook up alts, plus, there's a good number of good AH inscriptions out there. Still though, I have to wonder if it wouldn't have been more profitable to simply sell the plants and buy what the inscriptions. Thumb down for leveling and thumb sideways for maintenance.
Blacksmithing - none of my toons have this profession but my brother's warrior does and he ranks it with LW.
As a side note, LW, Tailoring, Engineering and BS all have some personal buffs akin to the inscriptionist shoulder buffs.
My inscriptionist hasn't dinged 80 yet so maybe those priest buff scrolls will prove uber useful but for now, I'm calling that trade skill as the one I've gotten the least out of.