One of the big announcements at build 2014 was Windows Phone 8.1 which offers a serious amount of functionality over and above Windows Phone 8.0. The new operating system is a significant update for the phone and is available as a developer preview for developers only. It will be rolling out with new phones shortly and we can expect it over the air as an update for everyone during the summer.
For me the big improvements are:
You can get full details on all of the changes here: http://www.windowsphone.com/en-US/how-to/wp8/basics/whats-new-in-windows-phone
To get Windows Phone 8.1 you must sign up as a developer, but it's easy, here's what you need to do.
(NOTE: There is no going back so do this at your own risk. This is the final release of Windows Phone 8.1 so it is stable)
Cortana is only available for US English so if you decide to use it please be aware that some location services may not work perfectly. I have been using it and it is pretty good if you ask it to "Find a Starbucks nearby". To access Cortana you must have Language set to English US, Region set to US and speech set to English US. If you do change these settings you may need to wait for the language packs to download and reboot your machine. Cortana is a separate app and is currently in Beta, so it's available in your app list and can be pinned (once turned on in settings/applications).
I won't re-invent the wheel check out this article that talks about how to project your Windows Phone 8.1 screen. You need to get a tool for your Windows 8.1 desktop as well as update drivers on your desktop too.
Best of Luck!
Thanks for the steer, works well -great new look, feel and functionality, thx Niall