[GoldieLocks]

I think its true that your only as good as your worst band member. Any musician is capable of ruining the groove for everyone (unless its the quietest instrument).
I think its almost impossible to ignore a singer with bad timing. The worst is a drummer with bad timing. You are legally allowed to shoot these people.

A very good musician I know told me years ago to STOP playing with bad musicians. Enough exposure to bad musicians will ruin your timing, intonation, dynamics etc. Its a dangerous thing. We don't always have a choice in this matter - but we should be aware of the damage it causes.