For similar reasons, I just can't bring myself to use OSX's tagging feature; it just seems like so much effort without a good use case. I'm not sure it helps that the defaults are simply colours, rather than real examples. And I don't really want to think about how files are shared (server, dropbox, google drive, usb stick) and do all the necessary research into how tags work in each and every case. I too would be interested to hear if anyone's successfully found an effective use for file-based tagging.
OS X tagging is sometimes handy for tasks over a short time frame. Picking out photos to upload to FB? Scan through them all and hit cmd-6 on the ones you want, maybe cmd-7 on the ones you need to crop. Sure you could use Bridge, Aperture, etc. but having it built in to the OS is nice.
I rely heavily on spotlight to find files I want, and about 99% of the time it works perfectly. Sometimes there is a file I am going to keep that I suspect will be hard to track down using spotlight in the future; either because it has to be badly named (source code files), will not be easily indexible (scanned pdfs or images), or my interest in it is not directly connected to the content of the document (i.e. a description of an algorithm with an obscure name which I have a specific application in mind for).
In these cases I use the tags feature to augment the metadata so that I am pretty confident I will be able to find it quickly in future, even if I can't remember exactly what it was or why it was originally saved.
