I've done Fedora 16 Beta RC2 LXDE spin testing.

That result is here. I would say it's works fine for me except "QA:Testcase audio basic" but lxmusic is an alternative choice.
Talking about doing Desktop test cases, "QA:Testcase_desktop_menus" takes long time for me. Of course it depends on your computer's spec e.g. installing process might take time. Basically I tired to do quick testing(I'd say that I did happy path testing) for every applications in the menu but not test deeply. Other tests take short time and not so difficult to do.
I usually do this flow.
1. Install a spin
2. QA:Testcase desktop error checks
3. QA:Testcase_desktop_keyring
-> I use a laptop as test machine, and it uses wifi connection(WPA2). Network connection is important to do browser testing :)
4. QA:Testcase_desktop_browser
5. QA:Testcase_audio_basic
6. QA:Testcase_desktop_automount
7. QA:Testcase_desktop_panel_basic
8. QA:Testcase_desktop_panel_advanced
9. QA:Testcase_desktop_menus
10. QA:Testcase_desktop_updates (installation)
11. QA:Testcase_desktop_updates (notification)
12. Re-install
13. QA:Testcase_desktop_login
Why I re-install a spin in No.12 is pre-condition of "QA:Testcase_desktop_login" is bit different from others. Although, install process doesn't take long time so that it is OK to have re-install step for me.