I travel once or twice a week to London for work from Darlington. Because the first flight doesn't get to London until 09.35, I am forced to use the train. I will be using the 05.50 bmi departure when it is running, but it is just for 2 weeks. I have to add I think the train is expensive, over £100 single if you wish to arrive in London before 10, and has been unreliable recently, twice having to get buses to/from Peterborough due to overhead line damage. (this may persuade some people to try the plane again?) I still think that with the right timings MME-LHR would be popular. Maybe a 4/5 times a day EMB-145 maybe the answer, I don't know.
On a positive note, I see the road signs are being changed over to say Durham Tees Valley Airport, about time too!