I have seen reports that the MD80 used suffered from excessive noise, especially at certain uncomfortable frequencies. The pictures I saw also seemed to suggest that the fan blades would not have been able to be feathered, giving extreme drag if one engine failed.
http://www.airliners.net/open.file?id=003461 http://www.airliners.net/open.file?id=166061
Note that it only had one UDF engine and was scrapped in 1994 (it flew at Farnborough 88 and 90)
It was built (normally engined) as the DC9-81/MD81 in 1979 - not sure when the UDF was fitted