Dave Marshall has written up a new post showing how he's used memcache, Gearman and Dojo to create an asynchronous progress bar he uses when generating large reports.
I have a (highly optimised) report that takes way too long to generate, up to around 30 seconds. [There's] too many variables to prime caches for every possible combination [and] personally, I don't think the browsers inbuilt progress bar is enough feedback for todays web users.
He generates the data into memcache when the user requests it and uses the Gearman worker processes to handle requests for data that doesn't yet exist. The progress bar is a part of Dojo and uses the dijit.ProgressBar widget to keep checking the progress of the build. This way the user can even leave the page and come back if the process takes too long with no threat to the generating report. You can find all of his code he's used to make it happen on his github account.