Assuming your customers are technically competent, allowing them access to the bug DB for bugs that might affect how they use or deploy your system is probably a good thing. On the other hand, access by competitors to your development plans is a bad thing (it's not always good for customers to have access to that, either). I don't know if bugzilla can do it, but what you really want is a way to mark bugs as internal or external, and allow customers (those who are registered and/or have a support contract) to search and view "external" bugs. If required, your sales and marketing folks can filter which bugs go from internal to external.
Cisco is a very notable example of this approach. Just about all bugs that might be seen by a customer are made available to customers who have an account with Cisco. Bugs found during development of new features and such are not exposed. Only a subset of the bug data is made available (not necessarily a good idea to expose names of developers, for example).