From PHPBB2 to PHPBB3 - is it painless?

Hi.
I just wanted to know if moving from forum version 2 to 3 was as easy as, say, click on a "convert now" button, or if there are preliminary security checks to be done, things/settings that get lost, in few words whatever is the "risk" of the operation.

Thanks.

You lost any customized CSS you have added. When you change forum version, the CSS is erased and replaced with new CSS. Some codes will not work on phpBB 3 if the codes were specifically for phpBB 2.

Also it is easy to change the version of your forum. Go to Hitskins and pick a phpBB 3 skin. When you install it, your forum's version will change, too.