How low cost do you want low cost to be, and how annoying are you prepared for it to be? I just picked (fairly arbitrarily) Monday 19th August, and although Expedia does offer a GBP18 Ryanair flight SXF - BRU you have to accept an 0620 departure time to get that, and of course no checked baggage and you need to include costs of getting to/from the airport. Given the need to arrive at least 1h before departure I would personally not even consider 0620 dep, and all the other flights Expedia suggests cost 90 quid or more. For the train loco2.com has one-way tickets Berlin Hbf -> Bruxelles-Midi from GBP63.50 at reasonable times.

As an American, I can only dream of having convenient train fares of about USD$80 to go between somewhat-distant cities. Berlin to Brussels for GPB63.50 (about $80 right now) sounds downright cheap to me.

Same here, I've been to Brussels quite often (for FOSDEM) and the difference is:

- flying: 120 EUR from Munich, getting up at 4-5, arriving at 9

- train: have to go the day before, have an additional night in the hotel (70 EUR) and THEN the train is more expensive than flying anyway. Maybe not so important if the company pays, but still not fun to argue (depending on the company).

Rubbish. I've travelled Berlin to Brussels (and then London) by train. It was very pleasant.

Sometimes you get a group of loud people around celebrating something, like soccer cup or getting married (especially in the connections with Regionals). Also last year there were often delays and problems in the connections between Mannheim or Frankfurt; I wouldn’t just call someone’s comment rubbish.

For every ride like that, you could get a teenaged school class flying in your plane.

While you're technically right, the MUC-BRU flight is 90% businesspeople in suits on the smallest regular plane I've ever used, I can't imaging TXL-BRU being different.

I.e. the chance of it having a school class in it is like winning the lottery ;)