iPaper: It's like paper...jabbed into your eye.

I personally would choose scribd over PDF, but the firewall my employer has in place blocks scribd. I still want to read the linked document so PDF becomes a necessity unless I use a proxy which could get me fired. Maybe that'll jump start my startup. :D

That's not the biggest issue for me.

Often the PDFs that get posted are interesting enough for me to want to archive and read more in depth on the bus, when I don't have an internet connection. Scribd makes this a royal pain in the arse.

Also, I strongly prefer the native feel of a decent PDF reader over a slow Flash UI running in the browser. (no, Adobe doesn't count as decent.)