Ace Monster Toys (AMT) holds Raspberry Pi & Arduino Nights every other Wednesday. Open to the public, come work on micro controllers, Arduinos, Raspberry Pis, whatever you want. Resident "expert" David R. will be on hand to help you get started, provide parts to build your own cheap arduino clone, give advice on your current project, or give ideas. Typically there's no specific agenda so feel free to come and just hang out and see our awesome space (and consider becoming a member).
AMT's meetup page lists all their upcoming Raspberry Pi & Arduino Nights and other activities:
Tell them Peter from the Berkeley Hardware Startup Meetup sent you. Questions? Email [masked]