You can have up to 8 bvi's per context. And, contrary to the conclusion of a recent thread, it is not necessary that each bvi have an ip address.
For troubleshooting purposes, it's obviously convenient to have ip addresses for all your bvis so that you can, for instance, ping addresses in the bvi's associated vlans w/out traversing a router, but it is not *necessary* to have one for each bvi. I have a context with 2 bvis, and only the first has an ip address. Works fine.
Regarding the default routes for multiple bvis, this is from the FWSM 3.2 configuration guide:
"The default route for the transparent firewall, which is required to provide a return path for management traffic, is only applied to management traffic from one bridge group network. This is because the default route specifies an interface in the bridge group as well as the router IP address on the bridge group network, and you can only define one default route. If you have management traffic from more than one bridge group network, you need to specify a static route that identifies the network from which you expect management traffic."
