Last night, I updated my iPhone and my iPad to iOS 5. To do a full upgrade, you need to upgrade iTunes itself (which I did on Tuesday), download the updates for the iPhone and then for the iPad, install the updates, restore from your backup (which took a very long time, mostly because I have over 300 apps installed), then Mac users need to upgrade to Mac OS 10.7.2 in order to complete the migration from MobileMe to iCloud, and then there are lots of updated apps to download to get full compatibility with iOS 5. It was a lot of work, and took me a lot longer than any prior iOS upgrade than I can remember. Having said that, this is a major update for the iPhone and iPad that adds a huge number of new features. It is well worth the time.
I am only now starting to explore all of the new capabilities of my iPhone and iPad with iOS 5, so I'm not ready to write about them yet. However, if you are ready to start reading today about iOS 5, you need to read Macworld. As you would expect, the Macworld reporters are all over this upgrade. For example, Dan Moren wrote this incredibly long and detailed post on iOS 5, and it is a great resource to learn about what is new (and something good to read during the long upgrade process). Serenity Caldwell wrote a great series of stories on iCloud, starting with this one. And Macworld is starting to post in-depth "Up Close" articles with on many of the marquee features of iOS 5, such as this one on the notification improvements and this one on iMessage. I'm sure that there will be even more great articles posted by the time you read this, so just check out the main Macworld page for the latest index.
I hope that you have a smooth upgrade to iOS 5!