On my BlackBerry 9700 (OS 126.96.36.1991) the site (StackOverflow svn revision: 6532) works reasonably well. Even dynamic features like adding/editing comments are no problem. Call me masochistic if you like. ;-)
In any case, when voting on a post, I get the orange
"An error has occurred - please retry your request." message after a few seconds. The vote however is counted just fine. Given the limited JS debugging capabilities of the device I can't really investigate more closely.
question.js this error message appears only once in the source, in a jQuery
ajax() error callback. This would indicate that the server did not reply 200 OK to the POST. Maybe someone with access to the server logs can spend a few minutes on this? I voted on SO question 2470907 a few minutes ago, if that helps filtering.