Our team used Mecanum last year with rather positive results, though its didn't feel very smooth to drive as the wheels fight each other, even when going forwards. We were not too impressed with the WPI libraries for Mecanum, we couldn't get them to work effectively, so we actually made our own libraries. If anyone wants to use/consult them, they can be found here:
http://ai-robotics.com.au/code-libraries/
For any help with them PM me, or send an email to the specified adress