The unofficial ChevronWP7 unlocking tool enabled side-loading on pre-NoDo Windows Phone 7 devices simply be providing the same kind of dev-unlocking you would get if you paid $99 for a developer account. While the tool was taken offline in January pending the talks with Microsoft, unofficial mirrors kept hosting the tool. When the NoDo update was pushed to devices, the tool became useless, as it doesn't work on NoDo.
And now we finally have a solution for people who want to side-load applications onto their post-NoDo Windows Phone 7 phones. The ChevronWP7 team will soon relaunch the tool, but this time with the full support from Microsoft, so you won't have to worry about the device re-locking itself after an update or sync. Unlike the previous version, this one won't be free - it'll require a small fee to cover ChevronWP7's costs.
I'm quite happy with this move. A small fee is acceptable, and it will enable homebrew developers to go wild, outside of the controlled nature of the Windows Phone 7 Marketplace. This will open the door to some serious WP7 hacking, but without the fear of being shut down by the next update. Developers who were previously wary of hacking WP7 will now jump on the bandwagon.
This leaves Apple as the sole smartphone operating system maker actively blocking homebrew. Palm's webOS has always been open to this, and HP is continuing this trend. Recently, several Android smartphone makers - no doubt pressured by Google - have announced that they will no longer lock down their devices. Symbian has always been open to this, so this means only Apple is actively blocking homebrew.