From 1998 until late 2002, my Amiga A1200 was my main machine. I used it for everything, email, web, word-processing - the whole shebang. Actually, it's quite mind-boggling how well it held up (or how I much I was willing put up with if you want to look at it that way :-))
Really it was only my inability to get hold of a GFX card that ultimately led me to drop it in favour of a Mac. The lack of CPU horse-power, was much less of an issue than you'd expect. The slow AGA and small screen-modes was the real killer for me.
There are a lot of computing tasks that have barely changed in the last 20 or so years, that I think an Amiga could cope with pretty well. I've yet to have a nice an email experience as I did with YAM back in the day.
With all that said, I always looked at my Amiga as a hobby as much as an every-day tool. It was always obvious they'd be a day when I couldn't blag it anymore.
But Life's no fun if you don't have a bit of a challenge ;-)