Hard to use without a full delete command.

I typically do:

Upload entire opml
Download entire opml to another PC
make some changes on the PC as I'm browsing/reading blogs
Upload entire opml from PC

Cannot do the last step easily. As a stopgap, if I could just delete
everything online just before the upload/import, that would be good
enough.

The main reason I would want a service like this is to synchronize my
opml across different PCs that I use regularly.

Being on the web means I could do it without firewall issues.

Very common to be working on a PC, add some RSS feeds, and then when
I am on another system, add some there. End result is a "multi-
master" replication/synchronization problem that no one has provided
tools to solve.

Also, in IE7 (and probably others?) can only inport/export the entire
OPML so there is no easy way to do incremental updates.