Both Adam and I use iView MediaPro to catalog and annotate our images. I'm pretty happy with iView's annotation interface, but its "Sync Annotations" feature, which allows you to sync IPTC information back into the source file, doesn't write IPTC in a way that will read properly in all applications. Most of the applications and online services I use seem to handle it properly (Photoshop, Breezebrowser, Smugmug, Flickr (which took some bug-fixing)), but I've not been able to get IPTC caption import to work with Porta (a slick, HTML/SimpleViewer online gallery generator) (see update, below). I really like Porta, so I've written to Porta's author, hoping that he'll look into iView compatibility.
*UPDATE* Google's Picasa pulls out IPTC properly, and works with SimpleViewer as well!
*UPDATE* Mikkel Stegmann, Porta's author, fixed the Porta/IPTC issue 1 hour, 35 minutes after I sent him an e-mail. That's just awesome.