Hi,
If you are publishing a new infopath 2007 form it does seem that you can publish as many fields as you wish, i have forms with several hundred promoted fields, though displaying them in one view is not a good idea.
The problem seems to be making changes to a form with high numbers of promoted fields, after a certain limit, typically around 100, the publishing of a new modified template seems to time out and give the updating content type failed message.
So it should be possible to promote as many form fields as you like, however this can severely restrict any further form development, unless of course you choose to remove some of the promoted fields or create a new library and re-link forms, and re-design and filters or default values in any forms that look at the original form library.