I've moved 'typical' virtual machines between hosts with VMware VMotion and not experienced any network related issues with clients accessing those vm's. Does anyone have comments about running a VM serving as a router(Vyatta, linux, BSD, etc) and any effects putting such a vm through a VMotion? I'm concerned the more constant network stream such a vm would be handling would have an issue.
Not a good idea.
The way switches (especially Layer 3) associate IP -> MAC -> Physical Port will get all sorts of confused when your VM moves for a short time. Even though VMware makes the process as seamless as possible, when you switch hosts you're essentially unplugging a physical CAT5 cable from the switch and plugging it back in a different port. For a router/gateway this is much more of a problem than a regular host due to the amount of connections and connection state that has to be recreated.
Depending on the switch, the downtime may not be severe, but rest assured there will be some lost packets along the way.