Granular feedback as to where they are in the process, setting expectation for time to completion
Feedback is a core quality of a usable form, but time to complete might not be the best metric. An expectation of how many more questions/sections the form has is probably a better way of thinking about it.
Might be a question of terminology here, but jquery progress bars IMHO should not be used for any form. 'Progress bars' provide feedback to a user about functions the system is performing, for example processing the input from a form, uploading a file, retrieving data from a repository etc.
A 'progress bar' on a form where the system is waiting for a user to fill in fields is useless and provides no context. Having said that though, there are other design patterns about that are similar to 'progress bars' and these really do work. Im guessing this was the type of pattern your question was actually about.
The steps left pattern will show a user how far they have come through a process, and how many steps are left, the system can also give feedback at intermediate points along the way to reassure the user that their information is 'right' (acceptable, complete, formatted correctly etc).
The checklist pattern is similar to a steps left approach, but it doesnt enforce a specific order for each part of the checklist. This pattern lets users pick and choose their way through the form.
The wizard pattern similar to the other patterns, but is useful when the steps needed to reach a final goal may vary due to decisions made in previous stages.
Ive tested a large number of forms, some simple, some with multiple sections, complicated parts and relationships and every test result I see is the same. A 'progress indicator' - usually a steps left, but sometimes a combination of all all 2 or 3 of the patterns I mentioned above help users complete the form.