I can’t tell you how many times I’ve done the Berlin-London trip early Monday morning before work. 2h might be an underestimate, but it really is quite fast.
The train is pretty much a full day. I've done it when schedule allowed but going down the day before, working on the train, and spending the night in a hotel as opposed to doing an out and back in a day doesn't work for a lot of people.
Of course, shorter segments of the Northeast Corridor work pretty well by train. I pretty much never fly Boston to NYC unless I'm under unusual constraints.