We use WP and Xenforo, although the Wordpress front page is very 'beta' as we're trying to switch to one of the Xenforo portals. We will still use WP for reviews, miscellaneous articles and advertorials.
To get recent posts on to the front of WP I made an extension to XF's RSS system to get more information in to it, then a plugin for wordpress to give a short code to display posts from the feed.
We use XenWord for user integration which works well except for privileged users (WP editors and authors need to be set up manually). It does allow comments and articles to be auto-posted in to XF.
The XF-a-like menu we have in Wordpress is based on one from a WP theme, but restyled to look like XF. The remaining mismatch and lack of notifications is a motivation for using an XF based front page, rather than a WP one.
A remaining issue was combined XF / WP search which we did by using Google Site Search as the frontline search tool for both sites. An 'advanced forum search' link then takes you to the normal XF search.
The integration is a slightly uneasy one, and our reviewers (ie CMS users) were a bit put out by the move, having been used to the VB4 system with the "publish as article" function that allowed them to write things in the forum area, rather than deal with WP. Their complaints led us to use email-to-article in Wordpress so they now send their work by email, rather than doing it via the forums.
Any use?