I doubt seriously that MSN or Adobe have any versions of their software aviable for the PS3.
I don't know all that PS3 can do on it's own, but I think it's just a web browser.
If you want to have more OS-like features you'll have to run Linux.
Here is a video of Fedora Core 5 running on a PS3
http://www.youtube.com/watch?v=_ZXcuhJkwx4
The main thing that sucks about PS3 Linux is you don't get 3d acceleration using it. However other then that it acts like a regular PC.
Would be good for things like a jutebox or a front end to mythtv or something. You can store all your music files on your desktop, but access them from Linux and play them there. Stuff like that.
There is Gaim (they recently changed their name to Pidgin) that works fine with MSN stuff as well as most other instant messaging stuff. (AIM, Jabber, ICQ, IRC, etc) And Linux has it's own PDF applications and such which are actually pretty nice.