As a newbee I just wanted to say Hi. My Arduino Uno arrived yesterday, I got the serial communication working just fine, really easy. Just waiting for the LCD shield to turn up & I can play some more. 
I'm going to link it to my solar panels & grid tie inverter to get live readings so that I can log the performance over time. All my kit is pieced together from relatively cheap bits so this would give me more control too.
I can run the grid tie inverter from batteries too however it is important not to run them down too low otherwise they get damaged, so automated control of this would be usefull too.
Once I've sorted out the control, the intention is go wireless so that I can remove the teather to the PC. Probably write a VB app later to give a wizzy front end.
Well, that's the plan anyway.
PS: sorry about the animated stuff, seems to vary between forums. 