Tritransit Area will love this...
From DCist, NYC-based TransportAzumah to start service from DC to Philadelphia & Wilmington (http://dcist.com/2009/11/new_discount_bus_options_to_philly.php)
The DC stop is Union Station and the cost is about the same as Greyhound with an advance purchase ($20 one-way, though there is a savings code in the DCist article). The schedules to Philly on Friday/Saturday/Sunday are very ambitious, hourly service from 7:00 AM-10:00 PM! There's a stop in Baltimore at the Baltimore Travel Plaza (5501 O'Donnell St.) en route.
The Wilmington schedules, done on an NYC/Wilmington/DC run, are 3 round-trips daily with a 4th Friday/Sunday roundtrip and a 5th trip Friday/Sunday heading towards DC.
I think this fills a gaping hole (not everybody wants to go to NYC), but will it succeed? I know some SEPTA fanning and maybe even a DART detour is in my future...
New Century has actually been offering DC to Philly service for the past few years with a $15 walk up fare. Although their service operates every 2 hours from 8AM to 10PM, every one of their Philly buses I've been on has been close to capacity. However, I believe most of the people stayed on the bus to continue to NYC.
It'll be interesting to see how TAZ will perform. From my understanding, not all of his trips are going to be operated in-house. Also from my understanding, he does not keep 100% of his revenue on his NYC/Wilmington/DC runs.
Yes, New Century as well as Apex has offered Philly to DC service for some time. However, all of those runs originate from NY, which means the buses are overcrowded - people literally cannot get on the bus. The last time I rode the bus, I was VERY LUCKY to get the VERY LAST seat on the bus coming from DC. On the way to DC, people in Philly were denied access.
I personally am very excited about this new service, and plan to use it sometime soon. Also, hourly service? Yee-haw I say!