I've had an S3100 for months now, and overall, I'm really happy with it. I used to use my PS3 for streaming and DLNA, but the fan noise just grated on me. The S3100 is totally silent (if there's no disc in it) and works great. The Netflix, Hulu Plus, and Amazon Instant Video apps aren't as nice as they are on the PS3, but I can live with that. I keep files on a SanDisk Cruzer USB drive (really small), and keep that plugged into the front USB port.
An unexpected bonus is that it will natively play .flv files, even though those aren't listed in the manual.
One nit that I have is that a disc will spin all of the time, regardless of if I'm watching something else. I wish that didn't happen because it's unnecessary noise, power, and mechanical wear.