Mixpanel is always looking for engineers to either fill out our backend team (working on a real-time data crunching datastore we built in-house) or on our front-end team (building out JS infrastructure to accelerate how fast we can build products for users).
Email us at jobs@mixpanel.com or head over to http://mixpanel.com/jobs
Check out our dev blog too: http://code.mixpanel.com