To be paranoid, there may be an exploit to influence the RNG. But that's really paranoid.
Yes - was already brought up - although am pretty sure if it was a problem with the major OSs then pretty much all of our BTC should already have been stolen (the thieves didn't waste any time stealing from the broken Java RNG implementation in Android - why would they not have done the same for others then?).
And people did run checks on the entire blockchain for the re-use of the random K values in tx's - apparently re-used K values only showed up for a very small number of tx's that were most likely from the Java RNG issue.
I mean on purchased used computers. A real long shot, for sure.