I have to say having tried several systems only to discover they are for Linux fanatics - or assume you know all about complicated standards etc, I went to Grovestreams who ARE free up to certain number of uses per month (large) and if you look at their example it uses Arduino strings - I simply stripped all that out in favour of char arrays... essentially it's a web page call with parameters including the values you want to send and an API key which you get off them at a touch of 2 buttons.... it's an absolute breeze to use. I set up 2 temperature inputs - there are dropdown boxes for operations such as averaging and interval which I didn't quite get until I set to AVERAGE - and intervals of an hour - and basically you can fire stuff off as often as you want to it - and every hour it will plot a point - averaging what you've sent in that time . Within minutes I had it running - and 3 days later I have internal and external graph plots superimposed on each other. Really, it's worth a look. I took a look at Xively a while back just after all that name changing - and decided that life is WAY too short.