Thats what i was told, maybe its all bunk
Discussion
I think they just meant your *privacy* would be leaked, just because everyone you accept payment from would be able to see all of your other transactions that use the same address.
That aspect, I completely agree with, but what was shocking when I heard it was the claim that signing messages with the private key could leak the key. This was either speculation of future quantum vulnerabilities through some kind of triangulation, or it was just plain bullshit. I've been acting on the first possibility out of reducing risk, but on second thought its a valid point since it would mean ecdsa is essentially broken (and it isn't, yet.)