If you've found one of these in a cache, please log it so I can track where it's been. After that, it's yours to do with as you will. You can leave it in the cache, move it to another cache, keep it, give it away, sell it, or (sniff) throw it away. It's really yours. :)
The exception to this is if you've found the special travelling version of the pathtag, which is clearly labelled, and won't easily be confusable with an ordinary pathtag. In that case, please move it on its way, as you would any other geocoin or travel bug.
My caching name is Ceolmhor. I adopted this handle long before I started geocaching. It represents the Scottish Gaelic word for "musical" (ceòlmhor), as I'm a Celtic singer and fluent in Scottish Gaelic. It was therefore natural enough for me to adopt a Celtic theme for my geocaching, and that led to the design of this pathtag.
This design was done for me by Cari Buziak, of Aon Celtic Art (http://www.aon-celtic.com).
I collect mainly pathtags of these sorts: Celtic art, dragons, penguins, native art, art masterpieces and spoofs, dragonflies and butterflies, and Colorado. I will consider other trades, however.