This weekend JQuery1.0 was announced. There have been hopes and dreams to add this into Drupal core for a while, but it was waiting on GPL licensing, then on a 1.0, and now on proper agreement that it works well. So far, GPL licensing and the JQuery 1.0 have happened. Now we just need to make absolutely certain that it works well as a replacement and/or simply as an addition. You can follow the progress and problemsin this issue.
There seems to be a few bumps along the way, but hopefully we can solve them.
Fast Path File System Cache - fastpath_fscache
The file based cache was an interesting issue. In HEAD, Drupal contains at least two interesting improvements: partial bootstrap using drupal_bootstrap and the ability to have pluggable cache mechanisms. The first allows a highly custom page to do only a partial bootstrap if it knows that it only needs to interact with a subset of the Drupal "world" (i.e. apis, objects, etc.). The pluggable cache mechanism allows someone to say "well, I don't like having my cache in the default location of the database because my database server is my bottleneck, so I'm going to use an extra module to cache my files to the webserver's disk which is much faster". It allows people on a shared host to get the performance previously available only to fancy/complex server's with a reverse-proxy. This is very exciting to me because several of the sites I work on are situations with 90% anonymous visits and where the database is a bottleneck (e.g. this site). In those cases this file system cache module should be a great addition.
Note that as of this post, the fastpath_fscache module is listed as being "beta" quality and not recommended for production sites. I'd love to see some performance numbers, perhaps using the guidelines that webchick put together in the handbook on HOWTO Benchmark Drupal Code.