Does DD-WRT QoS actually work

There have been various reports of DD-WRT QoS not working (here, here and elsewhere).

The DD-WRT QoS Documentation mentions some checks would indicate whether the proper priorities are being applied to the traffic. (Though it does not suggest a method to verify that QoS is actually taking effect…)

Has anyone checked their traffic priorities and found that the priorities are not being correctly applied, or that they have been properly applied but that did not seem to change anything? (Or, having enabled QoS, see traffic degradation or other issues.) Bonus points if you've actually quantitatively tested your QoS setup.

Just to clarify, I'd like to know if setting up QoS using the GUI works. (I'm using OpenWRT right now and I can just as easily use a script there. What interests me is if I can waste less time setting QoS up by switching to DD-WRT)

Answers I'm NOT looking for:

• "Just switch to Tomato/OpenWRT/X-WRT/Gargoyle/etc"
• "OF COURSE it works, why wouldn't it?"
• "Just use this script" (or some other script)
• "QoS only affects outgoing traffic and doesn't really help anyways"

UPDATE 2011-06-02:
There weren't any answers from actual DD-WRT users, but the prevalent opinion seems to be that QoS in DD-WRT (when configured via the GUI) is broken.

UPDATE 2011-11-29:
There's now a LuCi module for QoS on OpenWRT (not sure how long it's been around). I've done some cursory tinkering, if I notice any great wins/fails or can devise a test scheme, I'll try it out and report back.

UPDATE 2012-01-31:
Gui Ambros has submitted the best answer so far, and although many people still complain that QoS doesn't work, I also feel that QoS is a difficult beast to tame, so I'm always suspicious that it was not correctly configured if no testing was done. Accepting his answer. If anyone using a current version of DD-WRT can show that QoS isn't working, please submit a new answer!