We have used pneumatic every year you team has existed, i think if you know how to use them right and for the right applications they work well. There much fast than motor but there mainly limited to two positions.
Heres a link to our 2011 robot with a fully pneumatic arm and it was a very good robot. We won an event with it, one off-season event, two-time finalist (divisional Finalist) and semi-finalist at MSC.