I've been using phpbb2.x for about 5 to 6 years now. I've been hacked at least three times, but other than that, the open-source forum system has been good to me and my 35+ unique visitors that use the board monthly. It's been roughly 3 years since phpbb3.0 was released in late 2007 and I still hadn't upgraded.
I was worried. I had nearly 7 years of conversations and user information that could easily be damaged. On top of that, I've become so fluid in Drupal and Wordpress, why should I become familiar with another version of forum software? My ultimate choice was to upgrade to phpbb3 regardless and try it out.
The conversion process for me was going to be the most important. Most major open-source content management systems can now be installed within 5 minutes or so. My real issue would be to make sure the phpbb2 database was safe and properly converted to phpbb3. Included in phpbb3 installtion is a convert process from phpbb2 to phpbb3. Win! The best part is that asks for phpbb3 to be installed in a new location, keeping the old database and forum intact. Win plus 2!
The installation went perfectly and the conversion process took about 10 minutes for database with about 90mb. Adding a new style was easy, but modifications are a different story.
Just like in phpbb2, phpbb3 does not come with an automatic installer, you had to modify the source first with an automatic install mod. AutoMod was installed easily (formerly ExMod on phpbb2), as a matter of fact it was very easy, didn't need to open up any files like in older versions. I added about 10 or so mods I found on phpbb.org, about three did not install correctly at the first go.
So I was able to do so much more so much quicker than I was expecting. However, now I feel that I've hit a brick wall. I'm so used to being able to upload a module, enable it, then configure, set it and forget it. With phpbb3, things are little different. Example, for Google Adsense, there are several Adsense modules for Drupal. But with phpbb3, you have insert it manually in each template page.
Overall, I'm happy with phpbb3, but it is far behind the leaders Drupal and Wordpress. Granted, each Wordpress and Drupal are not nearly as close to having the same out of the box features that phpbb3 has for a simple operable forum system. Drupal would require nearly 10 additional modules to receive the same functionalilty. Perhaps open-source content management systems have a ways to go