HTTP asset-handling has been enabled (it was a menu item before but not used except for the map), and a Linden had this to say:
"From a performance standpoint you should begin to see better texture download times. Reducing our dependency on the simulator for these requests and eventually directing them to a services layer will also improve the reliability of those requests. Textures and objects represent about 90% of downloads to the Viewer. That means that any Viewer bugs that hamper the performance of textures and objects make a big difference when it comes to lag.
We found and corrected a bug in the latest version of Viewer 2.1. (This particular bug has been present for a while and also exists in the 1.23 code base.) The bug was related to object retrieval, and was causing object requests to bypass the cache and constantly make requests for those objects to the asset system. Generally, most residents frequent the same regions, and the objects in those regions are cached locally so that they can be downloaded very quickly, improving overall rez time. It’s only when objects are changed (not very frequent), or when you visit different regions, that a request for objects are made back to the asset system. So, download Viewer 2.1 and you should notice an appreciable improvement in performance."
The cache has been broken for years, but the HTTP asset handling is new. These improvements are reportedly going to eventually be included for 1.XX (which most people still use as it's better in many ways).
Are you using V2? It affects V2 only at the moment (well, Snowglobe/Snowstorm too but they are bleeding-edge). LL said at SLCC apparently that they don't have the resources to keep on developing 1.XX and are going to push ahead with V2. They spent 2 years and a megaft of dev time on it, and are now like a man with one foot on a log and one one the riverbank.