I'm not a legal bod but as I understand it in the UK at the moment, computer software copyright is similar to music copyright as opposed to book copyright which has a longer term to it.
If I understand correctly, music copyright lasts for 50 years from the date of the first publication/public performance and I'm pretty sure computer programs are the same.
At the moment, although it's not enforced and the government has said it needs to revise things, it's actually illegal to rip a copy of your own CD for your own personal use on an iPod etc. or as a backup. This carries through to software too and as such technically, it's illegal in the UK to use something like WHDLoad if you follow the letter of the law completely.
That being said, I don't think anyone is going to prosecute anyone for making a copy of your own original version for your own personal use and this is why the Government wants to revise the copyright laws because in a lot of ways in the UK, they're just too tight and un-enforcable.
So the answer to the question really is, it depends on the copyright laws where you are as to whether it's illegal today... or tomorrow. As far as I can tell, in the UK, Amiga games should be out of copyright sometime around 2035 onwards so it'll be just in time for my retirement
Paul