I use my Amiga4000T-060 mainly for writing my science-fiction novel (with FinalWriter 97). However, I usually have "Radio Rivendale" or "Streaming Soundtracks" or my MP3 collection of every Loreena McKennitt song playing in the background with AmiNetRadio. Similarly I use my Amiga for most things related to my book and as it's a sci-fi, that includes:
* drawing up tech schematics in PPaint
* playing with ship and station designs in Imagine or LightWave
* doing complex calculations in TurboCalc or MapleV (or both via ARexx)
* Maintaining a database of my characters in SuperBase4 Pro
* generating planetary maps with "Planet"
* generating solar systems with "StarGen"
* and doing research on the Internet with IBrowse
For some reason, I find myself to be more inspired when I'm working on the Amiga. Don't know why. I'm sure it's purely psychological but it works so I'm not going to change it. I've written 125,000 words in this book so far and only have a chapter and a half left (mind you, it's a trilogy so I still have a ways to go). If it ever gets published I'll be sure to let everyone here know.
I must confess, though, I do use a PC for some things pertaining to my book. Every time I finish a chapter, I email it to my work in RTF so that I can do quick edits in Word during my coffee and lunch breaks. I also use Celestia on my PC at home to simulate my universe in full 3D... nice... but I wish someone could port it to the Amiga so I could use it there. ;-)