>My USB mouse doesn't work with 7.0, there's lots of little cursor freezes in X
The latter was a problem with Xorg and FreeBSD, should be fixed already. The mouse, well the are some mice with problems especially those from Microsoft (lots of them fixed in stable, e.g. Microsoft Optical Notebook).
http://www.freebsd.org/cgi/query-pr-...ator=&release=
It depends more or less on the device, sometimes it's better in 6.x, most of the time it's better in 7.x. With the advent of 8.0 next year (or the end) we will see a news usb stack (USB2).
>pkg_add keeps buggering out
There are only 'two bugs': a bad mirror and/or the expectation for packages. The latter you will see at releases only or if you're following the stable branch (pointyhat-server -
http://pointyhat.freebsd.org/errorlogs/ - at the bottom).