My buddy Terry White turned me on to this technique that he picked up from Lloyd L. Chamber’s Macintosh Performance Guide (which is published online “for Digital Photographers & Performance Addicts”).
Anyway, Lloyd did a really great article on Optimizing Lightroom, and within it he specifically tackled the problem of slow JPEG exporting from Lightroom (if you decide to export a couple of hundred Raw photos as JPEGs, I can tell you from experience; it takes a while).
Anyway, after many hours of research (aided by his background as a longtime software engineer) he learned a way where you can just about cut the export time in half, by manually having Lightroom do multiple exports at the same time. So, if you have 210 Raw photos you want to export as JPEGs, rather than selecting all of them and hitting Export, instead you’d select 105 of them, set them to Export, then select the remaining 105 and then export those.
Since Lightroom can do more than one process at a time, it chunks away at both batches of images simultaneously, speeding things up pretty dramatically. In fact, he found that you could actually split the group of 210 raw photos into three groups, and it will chunk all three (but beyond three groups of JPEG conversions, it doesn’t work as well).
He also found that this works differently on different types of machines (for example, if you have just a dual-core machine, two JPEG exports at once is really about the max it will do without slowing things down).
Anyway, you can read his full article here online, but I want to take my hat off to Lloyd for sharing this information, and I’m hoping Adobe is reading it, too, and that Adobe takes more advantage of Lightroom’s ability to simultaniously process multiple tasks in the next version.