Poor point
"Let's say I sit down at home and write a little function, play with it, polish it a little and think, "That's neat" - and then a few weeks later I;m coding at work and find the same piece of code/method works well so I reuse it ... who owns that code? Did I just lose my "rights"? Did I have any "rights"? But this conundrum only exists because of the idea that code can be copyrighted."
Umm, no. I'd say there is about a 10% chance of there being any conundrum as it will almost always be covered by the documents that make up your contract of employment.
If you read this you will usually find something along the lines of "any IP you create as part of your work for The Company, or on systems and hardware owned by The Company belongs to The Company". So, do it at work -> theirs. Do it at home on your work laptop -> theirs. Do it at home on your own PC/laptop (and not SSHed in to/using software licensed by The Company) is your IP.
In that latter case you should keep a verifiable copy o the code 'at home' to prove it was created there first and, unless you get a legal agreement with The Company otherwise you are giving them implicit global rights to that code if you re-use it as part of your work.
See, not that hard really if you put your mind to it and actually read your contracts/know anything about IP law.