I feel your pain Melissa, though fortuitously I stayed at a friend's place in DC last night instead of commuting back to Baltimore, and I have to say that my level of happiness skyrocketed for the day.
It's great that we have Amtrak as a backup to MARC, though paying three times ($7 one way Baltimore to DC on MARC versus $21 on Amtrak) the ticket price is always a tough pill to swallow.
Looks like the problems today spanned the Camden and Penn lines. As an added bonus the MARC Tracker service, which provides riders with updates about delays, was down. Once again the delays were related to mechanical problems.
I've got a longstanding date to sit down with MARC Trainmaster Dave Johnson, so I'll try to get some answers from him on this latest delay and post them here on Stuck on MARC.