Certainly there have been a number of sightings of them but I personally think it is unlike to have the "power" or represent what it is commonly believed to. Mothman has been seen from the Crimean war(when 5 russians planned a surprise attack on the turks) to Point Pleasant to Chernobyl
I have seen the film and it is dire - it is an interesting modern take on the banshee though - the idea of it being a harbinger of death/destruction. Apparently the book is better as the screenplay was adapted to fit in with Richard Gere's Buddhist beliefs (he was producer and star of the aforementioned film)
Coincidentally, there was a guy who used to train at the same gym as me that we used to refer to as "Mothman". - This was simply because all the clothes he wore were full of holes, causing us all to wonder if he had an infestation. His name was D*** S***** (ahem, I would name and shame but he'd probably sue.)