Going by the language of IBs statement " A key test for infringement is a determination as to whether a substantial portion of the underlying work amounts to an expression of the prior work" It appears they may be preparing to base the case on the premise that Kier and Mike are utilising ideas and designs hatched amongst the vBulletin team. From my (admittedly limited) knowledge of cases such as this in the UK, they do not stand up very well. There would have to be very specific design documents etc to have any hope of standing up. The UK legal systems interpretation of this kind of thing is very narrow and specific. Even if the case is heard, it is a strong possibility that XF will simply be told to remove anything which is identical to previously planned work at vB (if that can be proven).