LN does not release data, although in an earlier thread there was mention that as at around October 2012 they claimed that they have had only a 'handful' of failures (as I recall 6) and all in relation to the single-row replacement bearings - none of their replacement dual-row bearings had suffered a failure. And yes, the result of failure is identical to a failure with the original bearing.
There was another recent thread where a member had his upgraded single-row LN bearing, installed by an 'approved' installer, fail after about 5000 miles. LN blamed the installer and paid for only a replacement IMS and bearing (perhaps understandably, they will not pay for collateral damage). UPDATE: It is actually a thread on perdrosboard and, in addition, it discusses various IMS upgrades:
http://pedrosboard.com/read.php?7,26540,26540#msg-26540
As I understand it, if the bearing is not seated properly i.e., perfectly flush, it will lead to movement/wobbles in the shaft and failure should occur very quickly - typically in a few hundred miles. If installed properly, then who knows how long it will survive? In theory, at least, the unsealed ceramic bearing should be more durable in a high-heat environment than a sealed metal bearing. Since Porsche does not sell replacement bearings, however, one has no choice but to go to an aftermarket supplier and LN seems to be the best choice. Certainly, for those with double-row bearings, I would rule out the Pelican Parts upgrade as it converts the double-row to a single row-sealed metal bearing with a spacer! Regardless, those who think that installing one these bearings is a full-proof answer, had best think again.
Brad