I have found there are quite a few problems with the VNC free ones. Mostly with configuration and lag times. It is still a good application for it, especially to get your feet wet with firewall configuartions and port re-directing. Kinda sucks if you want to control more then 1 remote at a location, because you have to change the port setting for each one and make the corresponding rule on the firewall. But it does what is says and uses minimal resources for the hooks.
I have found logmein.com works well for what I want, which is just remote desktop... I also like it for my family since I can tell them to expect an email from me. In the Logmein account, I can send them a message that will install the client for them and hook them into my account for remote. They only have to think of what they want their machine to be called.
The biggest problem with them is it only works for windows machines, no mac or Linux... It also runs in Java, and Java can have problems of it's own unrelated to anything else. And you also have to trust they are not poking around and monitoring what you are doing too as well as their own security is not flawed.