At Joe W, re: Shareware.
At a previous employer of mine I purchased out of my own pocket a bit of software to help me create macros so I could automate various overly-repetetive tasks to reduce the budding RSI I'd warned HR about.
Because I wasn't using it for commercial purposes, the program's author said it was ok for me to use it, but if I ever left the company then I needed to wipe it from their control. If they wanted to use it, they needed to pay for it.
When I was let go the company did not allow me to remove the software, even when I explained the fact that it wasn't theirs to use any longer. After a month of me constantly harping on them to delete it, but an ex-coworker whom sat in the cubical across from my old station reported to me that they were, in fact, still using it, I finally called the program author to inform him of the company's refusal to do the right thing nor to let me verify that the software was no longer on their servers.
The author thanked me; about a month later said ex-coworker informed me that the company was being taken to court for their stupidity.
In some cases causing your software to time-bomb-delete-itself is a bad thing, I agree, but there _are_ cases where "your" software is only yours by right of contract, a contract which the company you work for at the time is not a member of & thus has no legal right to use it after you & the company part ways.