Is there an RSS feed like https://serverfault.com/feeds/user/2561 but for answers only, for a specified user?
But, if you really want to stalk somebody, don't you want to know everything that they do?
There is now. I have created an application called Stack2RSS that converts API requests into RSS feeds.
A feed that fetches all of a user's answers looks something like this:
Example that fetches all of the answers posted by user #1 (Jeff Atwood) on SuperUser:
Parse their answer-source:
That will show you their most recent 10. Change pagesize to increase count.
Next best thing/workaround is to bookmark the user's recent tab and refresh every now and then. Now you'll not only be able to see their movements on answering questions, but when they comment and if they edit a post as well.