I rode the TransAm this past summer. I stayed at 22 Warmshowers Hosts' homes. I know this because I sent all of them Christmas cards this year...I was surprised by the number I had been hosted by! They were a big highlight of my tour. I made sure I arranged as far in advance as possible.
Warmshowers does have a feedback system. It is designed for both guest's and host's. I made sure I gave feedback on all those I was hosted by...all were wonderful! I think during the summer some of the Warmshowers hosts that are on the route and are one of a very small number of hosts for their town get overwhelmed with guests. If you choose to enjoy Warmshowers make sure you communicate a good length in advance...especially if they request that in their profile.
I am also a host, but live off the beaten paths. Yet we still host on occasion...my profile basically says give us a call, if we're home, then heck Yes! Come on over. I do check their profiles for any negative feedback...but so far none have been discovered and our guests have always been great!