I got a free 24 pass to try NowTv.com so I gave it a spin.
I didn't realise you can have two simultaneous streams which is nice. It doesn't allow for a third as you'll see below:
Needs a bit more app support but I tend to connect my PC / laptop into a TV via HDMI so its not really an issue for me.
If I didn't already have Sky I could see myself using it for the odd F1 race or football match when having friends over.