The steam producer allow you to produce more power using the steam than the power used to create it.
The biggest thing I saw with this is a self-powered turbine from Big Reactors, generating 28kRF/t for free and using around 1.8kRF/t to generate its steam.
http://i.imgur.com/AXFI56b.png

Yeah this is a known issue, I have spent may hours trying to find a way to balance this but sadly none are really practical..

It is not a exploit from the Power Converters. It is a Extploit from Big Reactors. But you can reduce the RF Generation rate in the BigReactors Config.