I'm not sure if I like OPML, don't get me wrong, I like the idea behind OPML but OPML as it is, is not that great. Why not? Simple, If I export my OPML file from my favorite news reader, it looses its category listings that I so carefully setup. Not that bad if you had 10 or even 20 subscriptions, but I have currently 66 RSS feeds (some people have hundreds, but I filter out dead subscripts on a fairly regular basis)
Now I know that in some cases my categories are not the same as yours, and thats fine. There could be an option during import to ignore/include the categories from the imported OPML file. Wouldn't that be nice? I think so. It would make backing up your subscriptions that much easier.
While on the thought of OPML, I would like to share my subscription list to anyone who would care, but it isn't easy. I have to manually upload it each time. Another nice to have would be an XML-RPC interface to load them into your blog automatically. This would have two benefits: 1) Users could see/download your subscription list and feel safe knowing its the most up to date. 2) Your website would have X number of links to other sites, helping in those sites rankings at Technorati and Google (other locations I'm sure)
Now if you read all the way down and have no idea what OPML is and would love to know what the hell I'm on about click here! ^^;