I am working out in the US atm and bought one to have a play with ($35 = £20 approx) - the tab casting is a bit iffy but for playing local content from mobile/tablet/desktop I have found BubbleUPNP to be pretty good. You don't need a full server install (unless you want to do transcoding of files that the chromecast doesn't support natively) on a big machine - client just points the local file and streams it directly to the 'cast. Works well and again, you can open up a web browser on your device and do other things as it streams in the background. couple of £ for the android client, think the rest if free and OSS (NAS installable too).
Only real PITA is that it must, at all times, be connected to the internet, even to stream local content. If you're on a hotel wifi with a sign-in page you're rooked. I have to bridge through a little pocket wifi router + laptop in order to get round this issue.
Other than that, can't be beat for £20.