Probably my biggest hurdle in getting started with Yii 2.0 (aside from getting my hosting company to upgrade my server from PHP5.2 to 5.4) has been understanding the changes to the application structure and the vast difference between the basic application and the advanced application. Since my personal site runs on a subdomain, this greatly complicated the issue for me. I needed something more than the basic application, but the advanced application was way too much overkill. I finally went with the advanced application, but now that I understand how the composer works to distribute the skeleton files, I'm looking forward to creating something that's between the two.
There is way too much to cover in a single blog, so this is just a look at the basic structure and front end changes that you need to know to get up and running in 2.0.
If you're past all of this and looking to dive into the nitty-gritty detail changes, I suggest you read the official documentation on upgrading.