Hi Marc,
If you save the events/announcements submissions to PW pages, then you have complete access to the API and can build a front-end editor for user to be able to edit their submissions.
Ryan posted this is the form builder forums as a way to save which user submitted a form.
You can access the User pages from the API, just like any other page, so creating a front-end profile editor is fairly straight forward.
I can post more detail here later if you need a place to start.