I use Microsoft desktop connection on my iPad (RD Client app) over a VPN connection with my Windows 7 desktop at work frequently. It works fine, although obviously the screen size of the iPad has some limitations. But it certainly works alright. I've also used SSH clients on iPads and iPhones for years to check in on linux servers as needed when away or traveling. Again, not ideal, but it works just fine.
P.S. There are a plethora of windows Remote Desktop clients, VNC clients and SSH clients for iPad and iPhone in the App Store.