A big problem with web security in the past was that it was impossible to have https-hosts with more than one certificate per IP. This is due to the protocol design of https, which needs to establish an ssl-connection with the certificate before the hostname is transferred.
There is a solution though, called Server Name Indication (SNI) and part of TLS. Strange enough, client compatibility isn't that much of a problem. Firefox, Opera and IE already support it in their current versions, konqueror will with kde4, I've no information when it'll hit safari. Oh, and I haven't testet w3m, lynx, links and wget yet, but if you want, feel free to add your experiences to the comments :-)
The problem was that until some weeks ago, openssl didn't support SNI, apachen mod_ssl didn't, lighttpd didn't. Only GnuTLS, but mod_gnutls is considered unstable by it's authors. With OpenSSL 0.9.8f, TLS Extensions and with them SNI landet in openssl, apache still needs patches.
If your browser supports SNI, you should see different certificates, all on the same IP. All certs are cacert-signed, they also have a Wiki page from the VhostTaskForce for SNI and alternative solutions.
Yeah, we already used that in the past. It's a »works, but ugly«-solution. It would mean that for every new customer we'd need to re-create the certificated.
Also from the sense of certificates, a cert should authenticate the owner of a page, not the admin of the server where the page is located. So I much prefer the SNI-solution.