For the most part it's standard PHP/Apache/MySQL compiles. We didn't really do anything magical to them, just gave the forums it's own kingdom and free reign over it. The old forums were sharing a box that was already quite busy.
When using the IPB topic import, all topics will randomly disapear from pages, requiring them to be recached to show again. Have tried different time settings, but can't seem to figure out what the catalyst is.