No caching other than regular HTTP caching. GeoServer comes with its own WMS tile cacher, but its incompatible with JOSM (it can't handle "arbitrary" bounding boxes).

Even if it were compatible though, I fear for the disk space it would use :D The dataset as downloaded from the USGS is about 30 GB in uncompressed GeoTIFFs. I've managed to squeeze this down to about 1.3 GB of JPEG2000 files, but a cache of the various zoom levels would easily balloon up a few more GB. I can only imagine how big Google's worldwide tile cache is o.O

I was blown away when the USGS began to offer 30 cm orthography in select areas, but this blows those out of the water in terms of resolution! This is truly a wonderful resource for those of you living down under :)

I may have once flooded the entire US (only in osmarender) by sticking an apparently bad tag onto the Siletz River.

A few days after adding "natural=water" onto the riverbank I randomly went to the tiles@home map and saw everyone was drowning. I knew that it hadn't always been that way, but assumed it was the result of somebody else's waterway edits. After we remained flooded for quite some time though, I removed the tag "just in case" and lo, the waters receded and the great flood was over.

Though T@H doesn't show any massive flooding in Oregon, it could still be a similar tagging issue.