Barry Diller got the go ahead a couple of weeks ago to split Interactive Corp into five companies. HSN, Lending Tree, Interval International, Ask/Match, and Ticketmaster will go their separate ways, now that objections from Liberty Media have been overcome.

So, now that these companies can go their separate ways, does it make sense for them to stay in touch? A quick look at our NetView data from April 2008 suggests that they shouldn’t tear up each other’s phone numbers, because there appears to be some benefit to the integration of units. In April of 2008, visitors to Ask, HSN, Lending Tree, Match and Ticketmaster seemed to be a lot more likely to use IAC’s sister properties than any random online user.

Take Ask.com, for example. In April 2008, 22% of online users visited Ask at least once. For those that also visited HSN, Ask enjoyed 32 percent reach. It was 34% for those visiting Lending Tree, 35% for those visiting Match, and 33% for those visiting Ticketmaster. Taking a simple average across the board (measurement sciences, avert your eyes!), IAC visitors were 52% more likely to have visited Ask than any random online user. More strikingly, IAC visitors were 226% more likely to visit Lending tree, and 207% more likely to visit Match.com than the overall online population (see table below)

So, does this mean that IAC has made a mistake, by splitting up? Not necessarily. IAC had certainly allotted house ad inventory to pitching its own properties (one analysis that we did a year or so ago had the number at about 20%). While this house advertising might have been effective, it may have also had an opportunity cost (lost ad dollars from outside parties). Secondly, there is no reason that the firms cannot work together in the future as separate companies. Further, allowing each company to focus on its own business without regard to its sister companies may allow them to be more responsive to the market.

So, is this the right move? I dunno. I won’t be betting against Mr. Diller.