Based on my DIY experience, I'd agree with jmh with a few caveats. The benefit of a pro in the case of drywall is that with the same level of quality, they can do 4x the work in the same amount of time as a DIYer. If you have a large area to cover, it may be worth it to you to hire a pro as they can hang, tape, mud and finish a garages worth of drywall in the time it'd take a DIYer hang the drywall only. Also, based on the wholesale sheet prices a pro gets, you may actually come out close to even - in many cases what you pay a pro for materials and labor to get a paint ready room is within a few bucks of what materials run retail.
Now, if you are talking a small area, it pays to DIY as you can pay a bit more attention to detail with out losing an insane amount of time. Also, some basic drywall finishing skills are a good resource for any Harry Homeowner.
The basement of my house was finished by the previous owner, who I discovered was a "good enough for government work" type. The sheets were hung vertically and I'm not sure more than one coat of mud made it on the walls after the taping the job. The benefits is that I don't need a stud finder as I can see the tell tales of every screw/seam. I know my work is not perfect but....
