You may have visited one of the other popular blogs about Joomla at alledia.com. It's written by a fellow Brit living in the US, Steve Burge (he is going to be a fellow instructor at the upcoming Joomla University in Chicago). He recently wrote a post phpBB3 Integration Can Be The Joomla 1.5 Killer App. As we often seem to do, he scooped me on a post I had started to write about the exact same topic, thinking about what Joomla 1.5's Killer "must have" application might be.
I think I might offer some different answers than his thoughts about forums though.
Joomla 1.0's Killer App
To consider this, we can check out the Joomla extensions site and some of the ranking used:
I feel I am pretty knowledgeable here at Compass about SEO, heck, I even wrote a book or two about it. I also know a good deal when we see one.
Last year Steve Burge of www.alledia.com came up with a new club concept, the Joomla SEO club. He had already written a great ebook about SEO, and then he bundled it together with online access and a forum to create Joomla's first non-template club!
There are three levels of subscription.
EBook Subscription
The User Subscription costs $37, lasts for 3 months and gives you:
SEO Forum access
Monthly Joomla SEO Newsletter
Access to the Joomla SEO eBook and all our tutorials
SEO Checklists to launch, upgrade and improve your sites
Joomla Corner 
