Adobe just announced the free Shadow software, which lets you simultaneously browse websites on your PC and your mobile devices (iOS or Android) - making testing during development of websites a whole lot easier.
It works by installing a mobile app on your devices (phones, iPads, etc) which listen for instructions from the Shadow software on your PC. In turn, the software on your PC listen for instructions from a Chrome browser extension. As you browse in Chrome all the connected devices follow along as you move around and change the site. Refresh the page in Chrome and the devices refresh too. Click a link to another page - the devices follow along too.
It's probably better explained by video:
I've given it a go and it works well and is easy to setup. I'll definitely be using it from now on.
It's worth noting that the Adobe Shadow app installed on your mobile device has its own browser built in. At least that's how I understand it to work. Apparently that browser is WebKit-based. So, if you setup Shadow to test on, say, an iPhone, iPad and a Galaxy S2 all at the same time, you're only really testing in the same browser but on different screen sizes.
Also, if you like developing using localhost then it won't work without use of some kind of DNS to point your devices to your PC.
I could be wrong on both counts above, but that's how I interpreted it. Still it's a great tool. Just remember it's not a replacement for properly testing sites on the native browsers on the devices once initial development is complete.