It would be nice to close keywords bug. I rely need UTF8 and space for tagging this.

And one more think. Don't you need to add keywords like this:
-xmp:subject="SomeKW1" -xmp:subject="SomeKW2"
instead of:
-xmp:subject="SomeKW1, SomeKW2"
I don't have any tagged photo with "non free" applications so I am not sure, but I know that f-spot uses first method, so that keywords are added one by one. Again. I am not sure, I need a sample tagged photo with some "standard" application.

digicam will support XMP. It is good idea to have some king of contact between this two projects. It looks like digicam will be the best on linux in this area.