I would certainly look into it. I regularly stumble upon words I don't know (or don't know the exact meaning of) either in my native tongue (Dutch) or in Englis

I would certainly look into it. I regularly stumble upon words I don't know (or don't know the exact meaning of) either in my native tongue (Dutch) or in English even though my vocabulary in both languages is extensive. Sometimes I write them down or store them somewhere but mostly I do not because it's not worth the effort. If it's easy to store words into this service, through an extension or a bookmarklet, it might work for me. A problem I come across with Dutch words is that there is no proper Dutch dictionary on the internet and I have to VPN into the university library to look up the definition, which is a bit of a hassle. Aggregated data of the users might also provide valuable information as to which words are generally considered difficult.