On the surface, the acquisition makes sense if you believe analytics will quickly evolve beyond its current claims-data world. That certainly seemed the trajectory of the industry until recently. However, many observers believe that Stage 1 Meaningful Use (MU) will dominate the Healthcare IT agenda for the next few years  and I tend to agree with them. If that's true, then Ingenix may have moved too early and made a bet that would not pay out for quite some time. Also, the commentary on HISTalk suggests revenues at Picis have grown less than $7M over the past few years and that the "$1B in 3-4 years" comment in the press release is dubious at best.
My personal impression is that Ingenix has made a speculative bet in the hopes that this merger will make sense a few years out. Part of the rationale may be the belief that if they pick up Picis before the stated synergies are operational, they may be striking a bargain.
As with most acquisitions, time will tell.
>>>UPDATE: Since I posted this, I came across this analysis from ZDNet that suggests this acquisition could be a positioning to improve Ingenix's ability to sell consulting and coding services. From the article:
But Ingenix hopes that its presence in the ER and ICU can give it an entree to sell consulting services and coding resources, as well as a play in the growing area of Health Information Exchanges (HIEs) — moving EHRs among hospitals and doctors under the emerging NHIN Connect standards.<<<
 There are some notable dissenters who believe MU is not all it is cracked up to be