Yeah as stated above, it seems like a shared proxy network would actually risk exposure of your network, whereas you are logging into your own systems and your IP shouldn't be exposed to anyone. That said, if you hop between your blogs on one IP/machine and Google happens to pick up on this (whether it be Chrome, Google Analytics, a browser extension, cookies, PC data through Flash, etc.), that could be an issue. You may want to create a VirtualBox virtual machine for each blog or at least have a private IP for each one. Unless you're managing them all from one central location, as it's not so much an issue then.