Hi Malcolm, replace the keyboard, monitor mouse? What do you mean? That's the whole point of the mini-- they can keep all that stuff and use it with the mini. That is precisely why so many PC users are switching, or considering switching-- and why the mini is sold without any of that stuff.
80 gigs is not huge, for sure, but likely plenty for most people (I've been working with 6 for the past three years-- and still had lots of space!). But you know what-- the cost of an external hard drive is cheap, and getting cheaper by the day-- so what's the big deal? Should anyone need more space eventually, just click on into the firewire port.
You are sure right about computers ageing; another nice thing about this mini not being horribly expensive.
Two USB-- sure, and two more on the keyboard-- enough for me, but otherwise a hub for $10.
And since you have owned Macs, Malcolm, you must know that you can not compare that 1.42 GHz across the board to a PC-- That's how many cycles, not how much work gets done. It's like saying this clothes dryer spins a hundred times an hour, and this one spins only 75, so the hundred one must get more work done, but not taking into consideration that the one spinning at 75 holds twice the load-- don't think that is the best way to put it, but there is plenty of information to clarify it for you on the web, if you don't already know about GHz.
I've researched well, and haven't seen anything about overheating etc. Only comment was that it could slow a little working with multiple large image-- sure, anyone doing serious work like that better get a heavy duty machine. This thing isn't going to do everything for everybody, but for most people it will do everything they need exceptionally well,
For sure most people are going to want to stick with their PCs, and be very happy with what they have. But the mini is a great alternative for those who want to try something different.