To clarify, the critical 2012 flaw is only on carbon bikes. It is due to the chain stay attachment tube being incorrectly bonded to the main frame, and the poor design means it is not well supported. If you look at a 2013 frame you can see the design has changed and the cross tube is now much more integral with the seat tube and supported with smooth webs to spread the load. If you go to the lapierre owners club site, you will see a large number of threads that show 2012 carbon frames broken in this fashion.
If you buy a 2012 carbon bike, and ride it to anything like it's capability it WILL fail in this area. Obviously, if you just ride it down a flat path at 3mph it will last a lot longer. Typically, they seem to fail between 3 months (heavier/harder riders) to 14months (lighter/ less serious) riders.
If you have proof of purchase, LP will replace the frame with a 2013 one under warranty without any quibbling, but as i mentioned, a lot has changed 12-13, so that can leave a bit of phaffing to get the bike back together.
Here's my 8 month old 2012 714:
The second issue is cracking of the chain stay itself, on carbon bikes this seems to be a bit of a lottery, with the alloy bearing housing insert coming unbonded from the hollow carbon arm. Possibly quality or process control related in production, but for 2014, all LP bikes now use an all alloy chain stay (even the carbon ones!). On the alloy frames, the swing arm crack appears to be in a slightly different place, and might be related to a tollerance issue, as it seems to occur in a "cross plane" direction (could result from over tightening of the pivot bolt).
Now, i have no idea what percentage of 2012 bikes sold by LP in the UK have actually failed in this fashion, and it will depend to a large degree on the loadings those frames are seeing (people ride very differently, under different conditions) but the owners on the LPOC site seem to suggest it's very very common on hard ridden bikes (and why are you buying a 140/160mm AM bike if not to ride it hard?)