I love Mike's plugin and use it on all my site. As I have been using it for a few years I actually prefer his older versions to the latest version. Each time that I have upgraded the plugin I have run into minor snags, which primarily related to permissions on my server.
However, if you are upgrading from a previous/older version to the latest version be sure to make a backup of your previous version in case you need to roll it back. When I upgraded recently to the latest version it did not carry across the settings from the previous version and all of my forms were lost. The reason for this is that they made significant updates to the layout of the settings page and have broken the settings into multiple arrays whereas in previous versions they were in a single array.
In my case I had to roll it back to the previous version because I had dozens of forms that I didn't want to recreate.
Fortunately, the plugin does have the ability to backup all forms in a single click so that when you upgrade you can then import your backed up forms.
All in all a great plugin with an excellent team of developers that work hard to provide a very easily customizable form with every option you could possibly need.