greatoaks->I've used Skylink. It's fine coming from the airport. Coming from town is a bit of a pain. There are two routes with no overlap, so each only has an hourly service. Basically, you don't want to get the timetable wrong. But a taxi isn't too much of a pain. For the city centre, as a general rule, if there's one or two of you, Skylink will be cheaper than a taxi. Three will cost around the same amount. Four or more and a taxi will be cheaper (although you may have to wait a while for a taxi that can take five or more).
Charlie->While I appreciate what you're saying, the time from Amsterdam to Brussels will soon be 85 minutes or so. That's not a huge amount longer than the Stansted Express and people still use Stansted while flying from London. And while there are other destinations in Belgium, the major alternative is Antwerp, which will be less than an hour from AMS. Bruges and Ghent will be a connection in Antwerp, while they also involve a not inconsiderable journey to Brussels.
Good luck with your campaign. I'm sure there is demand there for a service. Whether an airline can make a profit is the big question.