***UPDATE*** Microsoft announced that InfoPath 2013 is the last release of the desktop client, and InfoPath Forms Services in SharePoint Server 2013 is the last release of InfoPath Forms Services. See the Update on InfoPath and SharePoint Forms. Definitely take a look at Nintex Forms as a potential replacement.
I ran across this interesting post from Andrew Connell entitled My Thoughts: InfoPath 2013 & the Future of InfoPath. Great insight and thoughts about the future of InfoPath and where Nintex Forms fits in.
I get asked by clients frequently if Nintex Forms is a replacement for InfoPath. In my opinion, Nintex Forms is not trying to replace InfoPath. There is functionality that both offer (validation, BCS integration, repeating groups, edit/view in browser), but there are things that Nintex Forms does that InfoPath does not (mobility options, anonymous user consumption, workflow integration, browser-based designer) and vice versa (direct database access, call web services, nested repeating groups). If you have Nintex Workflow, then Nintex Forms is an amazing complimentary product that helps you extend your workflows.