i'm always surprised how few people actual know about vnc. its been around for a while. i use it at work to troubleshoot users' machines without getting up from my desk.
sure, its not the best remote control solution out there, but its broad compatibility makes up for that.
i use it all the time over the lan (which is fast and behind several firewalls), but i wouldn't use vnc over a wan connection. it's not really well suited for it when it comes to screen update speed and security features.
there are many features in vnc that can only be set by editing the registry. one that i use is the "AuthHosts" entry to limit the ip addresses of the machines allowed to connect to vnc. this would be a good idea if you are accessing a vnc machine from a fixed ip address, or you can at least limit it to the address range of your isp. another good one is the "AllowShutdown" option. nice to keep other users from being able to shut vnc off.
more here under "Advanced Options":
http://www.uk.research.att.com/vnc/winvnc.html
since i manage multiple machines running vnc, i have found this program to be very helpful to keeping track of them:
http://www.chronetal.co.uk/vncon/
it adds a nice "kvm-like" auto-switching feature and easier log-on to each machine. i use an older version of it myself, so i can't comment on this new version, but it looks similar.
there are now some commercial offshoots of vnc that allow greater security and other features. i have not tried any, but this one looks promising:
http://www.tridiavncpro.com/