Recently I had a survey appear on google/flights, probably because I use it quite frequently.. Anyway, the fact that one can't do mixed cabin class searches on outbound vs inbound flights was the "complaint" I submitted about the usability. I mean there a lot of times where I prefer to have Biz on the nighttime flight, but PE on the return daytime flight to save some $'s since I'm not going to sleep anyway.

It shouldn't be too difficult for them to implement, for crying out loud