Nearly one year ago I decidet to build a ppc amiga4000 to run Os4 after having used an A1200 for half of my lifetime. So I got myself a cheap A4000, a cyberstormPPC from ebay, and a Mediator, and a huge old(but cheap) fixed frequency 19" monitor.. My other option at that time was to sell my A1200 system and spend all of my money for an A1G3SE (as the XE was too expensive)..
But I decided to get an A4000PPC instead, mostly because Os4 was far away at that time and I would have spent all my money on a linux system (and I had already a linux system) but also because when I was a child and had a 500/1200, I always imagined how great the A4000 must be and I always wanted one..
At that time (last year) I didn't know that Os4 will be the last release for classic ppc though. So I was disappointed as hyperion said this, but later the microA1 was announced, and I though about buying one in addition to my 4000.. But I hoped it would cost something like 300-400Euros.. But as its more expesive its hard to find a reason to buy it..
I think OS4 will also be fast on a Cyberstorm(plus I can use all amiga games/apps), and for things like watching divx/dvds or playing games I can use my pc or ps2..
