just a quick one because it just drove me insane:
If you are setting up an openvpn server in bridge mode in a virtual machine on VMware ESX(i) hypervisor make sure to enable promiscuous mode on the vSwitch:
openvpn needs to be able to go into promiscuous mode to get the ethernet packets that are addressed to the vpn clients mac adresses. By default the virtual switch will prevent this for security reasons (arp spoofing).
If you are not comfortable with that use routing instead of briding openvpn configuration.