We have been working with Simon Perkins and Steve Souders on an open format for exporting HTTP tracing information. It's called HTTP Archive (HAR) and we have just finished spec v1.1.
The format is already supported by Firebug (with NetExport extension installed), HTTPWatch 6.2 and also DebugBar 5.3. Further tools like Show Slow and Cesium could be the next.
The key idea is to have a common format for archiving HTTP information that are captured by HTTP sniffers. These logs contain valuable info about page load performance and can be further used to analyze and optimize weaknesses of the monitored page.
There is already a few blog posts about this, explaining all details and so, let me just summarize the most important links here.
HAR Discussion Group (first post moderated)
HAR Viewer Online preview of *.har files.
NetExport Firebug Extension for exporting HTTP logs.
Recommended Firebug Configuration: Firebug 1.5a26+, NetExport 0.7b5