Definitely avoid 'Ski Road #2' which goes from the bottom of the Mosta lift by Shiligarnika, (i would say down to but it's basically flat) along to the gondola mid station and the top of the Chalin Valog runs... Also the Bansko run number 1 back down to the village can be flat in places, but would definitely not let the few flat spots put you off going down it and getting the gondola down instead! Apart from that I don't think there is much else in the way of long flat sections in the resort.
Ski road #2 is ok if you have a well waxed board and the snow isn't too slushy - I use it as access to Chalin Valog. You need to keep as much speed as possible though as you head past the bottom of the lift. Don't bother trying it if you're a beginner though as you'll end up walking.
Matt
Totally agree with Ms Fidler ?? runs are completely unsuitable for snowboards, the lifts are difficult, and there are no seating areas mid piste... there is a total lack of mirrors to 'check your stylee', and the local hairdresser has never heard of dreadlocks......
Much better to go to Borovets, or anywhere else.... and leave Bansko to real skiers who actually carve their turns instead of side-slipping..... (sorry, couldn't resist... been a long week)