If you have upgraded to Mango, your browser is now IE9. The browser control has been engineered and tested for backwards compatibility, but if your Windows Phone 7 (pre-Mango) application uses the browser control and suddenly finds weirdness, please do let us know.
The computer thinks these might be related:

Actually I think I found a problem:
I load a page (OAuth login) and then inject some JavaScript to make it more mobile friendly (I don’t have control over that page). What didn’t work before, but does now, is setting the zoom. Great. But as soon as I click a text field while the zoom is enabled everything goes haywire and the browser zooms to strange places…