Changing profession isn't something to be done lightly -- you lose all acquired skill in your existing professions, as well as any recipes you've learnt. On the other hand, switching can have its benefits -- if you're not needed as a guild enchanter after all, you can save money by picking up gathering professions and loading the AH up daily. If you're bored of running around levelling a gathering profession, you can switch to a crafting profession, though you'll probably need some spare cash to make the change.
Have you ever changed professions? Did you regret it or have you not looked back since?