A quick search reveals they've had these problems since ever (both duplicate spends and ignoring coinbase maturity).

It's possible that more people are mining to their MtGox addresses now, triggering the coinbase maturity problem.

It's possible also that the two problems are related (failed transactions lead to more failed transactions), and that the problem is exacerbated now that it has caught the public eye and everyone (including me) has rushed to withdraw their BTC.

That still doesn't help us if they lack the technical competence to solve this. Their inability to effect a fix is astounding.