I wrote a similar review about a month ago. That review has hanged in the system as "pending" for over a month, so I am writing a new one to replace it.
I am happy with Cornell's workmanship. We contracted them back in spring to reshringle our townhouse complex. So far no leak, so we are happy. The big test is coming winter, and we will see.
What we are not too satisfied with is Cornell's administration. Firstly, there were a few loosen shingles (after a major rain strom) that we asked Cornell to fix up. I don't know if they have fixed them as I have not heard back from them. Secondly, we paid Cornell in full right after the job was finished (Mike picked up the cheques personally). However, we didn't get an invoice until 3 months later, that was after many phone calls and emails by various homeowners. We need the invoice to claim the home renovation tax credits and for warranty, so we were nervous for a long while.
One more note: unless you get Mike's PERSONAL cell phone number, you won't be able to talk to a person on phone. They didn't return my calls / voice messages about the invoice and the loosen shingles that I left on the published business phone numbers. We finally talked to Mike because one of the homeowners had his personal cell phone number.
I would recommend Cornell for roof reshingling based on their workmanship, but you may consider insisting on getting the invoice prior to paying them. I also highly recommend getting Mike's personal cell number.