For those with developer unlocked devices, you may be interested in Heathcliff74's new tool found at XDA. Called 'WP7 Root Tools' the app is a very early release of what promises to be quite the full-featured registry editor, file explorer and tweaker app. More importantly, with this first release he's given us root (or at least near root) access on Samsung devices, something that has proven difficult so far in the homebrew scene.

This is the first release of a tool, that I've been working on for the past months. With this tool you get root-access to parts of your WP7 device. The first release only contains a registry-editor. The file-explorer and certificate stores will follow.

This tool is in alpha stage. That means that it is not feature complete and it is not yet properly tested. This tool also provides you with high privileges with which you can alter low level settings and data on this device. All this may result in unexpected and undesired behaviour, which may ultimately damage your device. Use this tool with care and use it at your own risk. The developer of this tool cannot be hold responsible for any kind of damages, caused directly or indirectly by using this tool.

The current version of this tool can only be used on Samsung devices. A small part of the code uses Samsung-specific functionality. The performance of the tool may sometimes be slow. This is the result of the way access to the system is elevated. The goal is to make this tool device-independent and to elevate access more directly in the future, but that requires more research.

Before forewarned though: if you're not a developer or know your way around registries, don't tinker--this can seriously screw up your phone as it accesses some pretty deep level stuff. Having said that, devs can now go deeper in writing apps for the phones, getting access to areas of the device not yet achieved.

Source: XDA; Thanks, Tobias, for the heads up