It has more than 200 updates on the i05. Some of the major points are these:
You can get instant access to Facebook and your contacts will be integrated.
IO6 will integrate easily with a number of other sites such as film and restaurant review sites.
For its phone app, several improvements have been made such as the Do Not Disturb mode, and if you get a call on your phone you can answer it on your Mac or iPad. It will also be possible to use it hands-free in many systems.
The new VIP emailing feature is popular with a lot of users - this highlights email from your chosen list of contacts, ie the people you most want to hear from/prioritise.
There is also a Passbook, an app that collects all your online loyalty cards, discount coupons etc together so you can access them easily. You will also be able to access them when you need them - the app knows where you are, so if you need a restaurant coupon, for example, you can get it out when you need it.

You can find more information here.