My favorite quote from the bus driver on my last trip to DC:
"We'll soon be down in Washington, DC...if all goes well."
Hold onto your wallet and bags as you try not to interact with the interesting people scattered throughout the terminal. Don't forget to go through the security checkpoint before getting on the bus - you may not even know that the mobile counter is the security checkpoint until they start yelling at people for not stopping. Not exactly first class, but especially if you catch a sale it'll get you where you need to go for cheap...if all goes well.