It does...at our Catholic Church (every year) at Easter we have new Catholics baptised (or if they've already been baptised in a Christian Church - they recieve all their sacraments (usually about 10 in total) and I'd say almost 70% were from Protestant Churches - we've had some Jewish converts and the others usually weren't raised with any religion.
We have something like 26 people in our RCIA program this year. A lot. I'm not sure the mix. Some will no doubt be coming out of various other churches, but some are probably unchurched as well.