From my end-user perspective there are some differences in approach but its nothing that can’t be learned intutively, just as with AllYouCanUpload.com.

Also, I found that the designs of both appealed to me for different reasons. I liked the spareness of AYCU, and I enjoyed the unified design approach to imgfly.

I’d encourage people to try both and use what works for them. They both offer a great free and unfettered service whose time may have come.