ZeroKlown...
I can't give you specifics, but yes, St Mary's County does have DSL (verizon?) and wireless. I'm sure others will provide the details you need.
I can tell you that the quailty of the technolgy you use depends a great deal on where you connect. Some areas are good for DSL, others are good for cable.
For example, I live in Hollywood (about 2 miles from the cable company) and I've enjoyed great service since day one (March 2002). I've never needed to call their customer service, so I can't speak to that. I think Oz can confirm this based on his experience.
Previous thread in this forum have beat this topic to death. Rather than repeat them, I'll let you refer back to them.
I do know that GMP has just started a major cable upgrade that should improve service. The Hollywood folks are the lucky ones here - that's where the upgrade starts. I don't know when the work will be finished though.
In any case, good luck finding a service you're happy with.