I looked at the code quickly and it looks like you can still limit attachement size. This is done via the Group Quota limits which can be set in the Admin screens.
However, since this is a group level thing, there is no easy way to get this information to display in the templates. Your users will have to try to upload a file and then get the max size from the denied error message.
FWIW, there is no way to limit a user to a total amount of data they can upload. E.g., userX can only upload 5MB of files.
As I said, this is from a quick look at the code and not actually
testing it. YMMV.
[originally posted on jforum.net by monroe]