I'm about to get to level 60 and I've leveled up Blacksmithing to 285 (I also have Mining)
I've read that no matter if you go for Armorsmith or Weaponsmith, you won't be using any of those after you get to level 80 since the gear is not as good compared to what you get raiding and is a waste of materials that are better off sold at the Auction House.
Is that the case? Is it really worth nothing? Do you think it's a good idea to drop it and start a brand new profession?
Blacksmithing on its own is a good profession. It gives you extra sockets (gloves and bracers) and if you farm the epic recipes, you can earn a lot of gold. This is the case with my dk - I have all icc and toc recipes and whenever I'm in the mood to earn some money, I spam in the trade chat and offer my services.
The two specialisations however - armorsmithing and weaponsmithing - aren't good. Those aren't necessary, since the pre-icc gear can be obtained mostly from fos/pos runs and from the EoT vendors. The two specialisation require a lot of materials and the items you would get from them will be easily replaced.
Soo, if you want to stick to a good profession, keep BS. Just don't spec it, unless you care about transmog.