I am currently implenting Exchange 2010 with 2 CAS servers using WLNB. I believe everything is setup correctly as far as autodiscover goes. The internal DNS of mail.domain.com is pointing to the VIP. The FQDN of the CAS array is outlook.corp.domain.com so that part is different although they're point to the sam VIP.
The problem is when I do a reboot of one of the CAS servers. Basically whichever is active. I did get an authentication box the first time I noticed it, but when I disabled the NICs on CAS1 server, nothing happened, although I did see a Reconnect so it seemed goo. I re-enabled the NICs on CAS1 server and then disabled the NICs on CAS2 server. Outlok then disconnected entirely and wouldn't come back up. Meanwhile ping the VIP of the WLNB never lost a beat.
I haven't messed with the permissions or authentication on IIS, but I haven't started migrating users over yet so I'd be willing to change some of this stuff if anybody has suggestions.