While I have not used this resource in class, it takes a type of project that I do with my students and puts it in a readily available web resource. I like the use of COSY and DEPT spectra as this is an area where students do not generally have ready access to these type of spectra. The number of total problems is impressive, and the ranking by easy of solving is very handy. If students are understanding a subset of the beginner problems, they can easily find more challenging ones.
I agree with the peer reviewer comment that the IR spectra should not have a zoom to a particular peak feature. Since chemists look at ranges of peaks before settling in on a particular peak, an improvement might be to have the students zoom in on the range of 1500-1900 cm-1 to guide them toward looking at carbonyls and alkene double bonds without giving the exact value.