Recently completed the GS technical assessment. It was not bad! I liked the programming bits (in that I got the questions, and they were straightforward), but the math section was pleasantly challenging and refreshing.
The math section provided an opportunity to review and refresh lots of topics I have learnt throughout university and high school, including calculus (multivariable), combinatorics and counting, linear algebra, and statistics.
In particular, it was fun reminiscing about Lagrange Multipliers, and all that!
http://web.mnstate.edu/jamesju/Fall2011/Content/M323LaGrange.pdf