I've gone to a number of hackathons in NYC in the past few months. As a designer you have to be very versatile. If you are a designer with front-end chops like me, you will be in VERY high demand since you have a good idea of the LOE for design implementation in HTML/CSS/jQuery.
Also, many back-end devs like to use bootstrap in interest of time, so knowing when/where to use custom design elements vs. using native bootstrap elements helps a lot. I've personally worked on bootstrap projects as well as 100% custom-designed.