Worked for me (currently at least) too, Werner, thanks.
Interestingly, I had created a workaround using Yahoo Pipes (that is,
ported in the delicious feed into the pipe, than used the pipe feed in
Feedburner), which originally worked and stopped working over the
weekend with the damnable 999 error. So I tried the change rss to
atom fix on the delicious feed and it's now working.
I think it's a little disingenous to be using the excuse "We have been
trying to contact the right people at Yahoo to solve this problem..."
as it's obvious that the problem is on Feedburner/Google's end and has
something to do with the migration. Why doesn't Google simply revert
us back to the "old" Feedburner, and go build a sandbox where they can
work out these problems without impacting their users.