So, it’s now 2010 (almost). Two of the most heavily used non-Free programs on Linux would have to be Adobe Flash Player, and Skype VOIP client. While neither have open-sourced their offerings, both do offer Linux versions.
The down side is they only offer 32-bit versions.
After several years of AMD64 bit Linux (the Debian port to AMD 64 has a mailing list that started May 2003 – over 6.5 years ago). Skype have repackaged their 32 bit build in a package that has the correct dependencies to run on 64 bit Linux, but the executable is still 32-bit. So no clean 64 bit system! Boo hoo.
Come on Skype! Come on Adobe. Either keep up (6.5 years!) or set it Free!