I purchased two Linksys RVS4000 routers, all the right features are there but they do not work together in harmony.
I have a customer that has two offices, both with dynamic IP's. This router supports the DYNDNS.com feature. It also supports site to site VPN's (AKA gateway to gateway). However it does not support site to site using dynamic IP's. For that you need the next model (RV042).
The irony is if you are using the RV042 are more likely to have a static IP's anyway.
So bottom line; An OK router though not exactly a polished product.