There has been lots of talk recently regarding the future of InfoPath and the gist of it is that SharePoint 2013 workflow will not work with InfoPath for interacting with the workflow events, it seems SharePoint 2013 will now deploy standard aspx pages which can be used to interact with the 2013 workflows.
This provide somewhat of a problem as InfoPath can be used rather heavily by some companies (including mine) and this means a difficult upgrade path.
K2 smartforms appears to be a direct solution to this, however it is still in its early versions and has some way to go to provide a rich design and client interface.
http://www.k2.com/blog/k2-smartforms-vs-microsoft-infopath