There's a firefox bookmarklet you can put in your toolbar. Click "share" and up pops a little window, where you can add a description or not, and send it off. La de da, it's all done. That is the ultra-low-effort process I've been craving - the potential energy barrier is enough lower that I may actually use it. They don't have comments at tumblr: their blog makes some ambitious claims about what they have in store ("We’re cooking something up. It’s taking some time, but we think it has the potential to be something hugely significant to the web") but for this specific purpose I might be happier without them.