Mick,
What is the function of the IPTC encoding option in PM4.5? What does it matter which you choose? And what happens when you check the write as unicode option?
MacRoman has always been the default since 4.1.x so if everything is working fine for you and those you work with, then leave it alone.
Some people (non-english speaking) may want to use a different encoding.
Unicode makes the IPTC record be written out as UTF-8 data and is a great way to completely internationalize your IPTC data (meaning everyone in every country would be able to read each other's text and have it display properly) but some applications don't handle UTF-8 encode IPTC records, including Adobe's Photoshop CS3.
If you're using XMP instead of IPTC then you're always using UTF-8 Unicode. Strangely enough, while PSCS3 cannot handle UTF-8 encoded IPTC, it works really well with XMP data that has always been UTF-8...
-Kirk
