Well, Mrs MawkSE and I were at the JW from 7/11 - 7/19 (That is before, during, and after Emily)... We stayed on the top floor (1442) with Club 91 - great experience and worth the upgrade fee to us. The storm started to move in SUN after 4PM, but 50% of the guests had cleared out by then. The Weather Channel and FOX News were both at the JW and all broadcasts we saw were based from the pool area.
The hotel staff did a great job of keeping us informed and allowed guests to stay in their rooms if preferred. They also created sleeping and dinning halls in the innermost part of the conference center. The only interruption of services was SUN evening (during the Hurricane) and until mid-MON where all restaurants were closed and no one was allowed outside a very confined area for safety. From 12a - 4a the wind speeds topped around 80mph in Cancun. Actual landfall was 60 miles or so south near Tulum. By Monday afternoon almost ever inside service area had been restored and Tuesday morning almost everything outside was open and accessable. The only exception would be some beach errorsion that I am sure the hotel and government will address very soon.
Marriott's CasaMagna did not fare quite as well. It appears to be older than the JW and did suffer some damage to the lobby, pool area, and several rooms. Nothing too serious though.
And last, yes parts of Mexico are 3rd World like - but Cacun is a great resort area that the MX government and private companies have invested heavily. I prefer it over several other Caribbean areas for a vacation destinations. But just like most of those areas, if you go off the tourist beaten path you will find very unwelcoming conditions and poverty.