I would have to say it depends on the Terms and Conditions of the software.
Personally I see nothing wrong with using second hand software. If the software was OEM then they are within their rights to stop you using it on a second PC even if its removed from the original one. It is meant to die with the original PC, of course this is mainly where Operating Systems concerned though you can get OEM copies of many other types of software, wasn't so long ago I bought an OEM copy of Nero the CD burning software.
But, even with OEM software, as long as you didn't register it it would work, of course you couldn't get the updates but it would work.
I have had bother registering some games that I bought second hand and to be honest with you I gave up and just never registered it. They either wouldn't believe it was removed from the original PC or refused point blank to register it in my name. The last one I had this bother with was Half Life 2 which has the Steam software on it to stop piracy. Now any game that has this software on it I don't buy its as simple as that.