Maximum limit of Vanity Domains

[Prasenjeet Pati]

Hi All,
I have been using Bind 8 but till recently never needed to create a large number of vanity domains.

I have a client who wants to create a very large (maybe a few thousands) of vanity domains. This is primarily a free web hosting
service kind of a situation where every user that registers needs to be alloted a domain of the kind user1.domain.com,
user2.domain.com, user3.domain.com and so on.

Please let me know if
    1) There is a limit to the number of vanity domains that can be created.
    2) Since all these will be pointing to the same IP, if there is a way to create default domain name. For example, is there a way
I can tell Bind to resolve  <anyname>.domain.com to a particular IP. This way, I can avoid the need of creating new record for each
new entry and also avoid restarting of the Named daemon after each addition.

Any help or references will be greatly appreciated.

Warm regards and best wishes to all.

Prasenjeet Pati