I definitely find myself compelled to keep my Remember The Milk (RTM) lists empty. It’s too bad the app didn’t work out for you!

If you dedicate one of your lesser-used browsers to RTM (e.g., Opera) it’s as useful as a desktop app in not getting lost in the Firefox/Safari tab shuffle while you’re working.

If you set up one of their Smart Lists you can work until a specific list is empty (Today, or a particular project or context), which has to be the major requirement for me. An app isn’t helping me if it’s showing everything I’ve done, or will do tomorrow, at the same time as the tasks I have to do right this minute. As I mentioned in my blog post (that you graciously linked!), it’s a lot more motivating to work toward an empty list than a page full of check-marks.

RTM does support multiple tags per task, projects (just add a new tab/list) and team collaboration. Unfortunately, their collaboration so far only allows sharing tasks with your contacts opposed to sharing your entire to-do list publicly.

You mentioned their Twitter and iGoogle integration, but forgot to mention their iPhone (”trouser Mac”) interface — which is beautifully done:
http://www.rememberthemilk.com/services/iphone/

They also work with Google Gears, so you could sync your laptop before a flight and knock off some coding/writing/thinking tasks on the plane.

Maybe it’ll get another look from you down the road. I’m certainly a convert.
Good luck with Things.app!