The main issue for me is that they only work in the url bar not the search bar. For the same reason people are upset about the favicon thing I don't want anything (mis)typed in the urlbar to be sent to a search engine. I've failed to find the correct setting to make this happen a few times before but just looked again and setting keyword.enabled to false prevents it from searching from the url bar (the setting is confusing and not related to the search keywords feature).
I did try firefox search keyword anyway once a while ago but it isn't that easy to configure and the setting were lost not too long after I started using it (I don't remember the details but I think my profile was corrupted by ecryptfs and the keywords didn't import to a new profile or something like that). Not importing them isn't a horrible choice (if that is what actually happened) considering there doesn't seem to be an easy way to even list them, but there should at least be a distinct import/export for keywords. The search page of preferences has a keyword field next to search engines but it doesn't seem to actually list them nor can you add a keyword from that page. All in all, it doesn't seem like a feature Mozilla cares about at all, although it would be a nice feature with a bit more work. Use from right click search on text selection would be another thing that would make it much more useful.
I tend to use ! in two circumstances, one as others mentioned when a DDG search didn't return what I wanted (and I am fine with letting DDG know that since it is the exact same search I just searched DDG) and secondly when I am looking for something on a particular site. Some of the second case would be best done via Firefox keyword search but the advantage of DDG is that they have a lot of obvious names going to the obvious place so rare specific searches are much more convenient than doing anything to set up a list. Since I very rarely use such searches, there isn't anything DDG could learn about me from avoiding just those searches going to DDG. OTOH, using site searches more frequently would be a win for privacy.
I did try firefox search keyword anyway once a while ago but it isn't that easy to configure and the setting were lost not too long after I started using it (I don't remember the details but I think my profile was corrupted by ecryptfs and the keywords didn't import to a new profile or something like that). Not importing them isn't a horrible choice (if that is what actually happened) considering there doesn't seem to be an easy way to even list them, but there should at least be a distinct import/export for keywords. The search page of preferences has a keyword field next to search engines but it doesn't seem to actually list them nor can you add a keyword from that page. All in all, it doesn't seem like a feature Mozilla cares about at all, although it would be a nice feature with a bit more work. Use from right click search on text selection would be another thing that would make it much more useful.
I tend to use ! in two circumstances, one as others mentioned when a DDG search didn't return what I wanted (and I am fine with letting DDG know that since it is the exact same search I just searched DDG) and secondly when I am looking for something on a particular site. Some of the second case would be best done via Firefox keyword search but the advantage of DDG is that they have a lot of obvious names going to the obvious place so rare specific searches are much more convenient than doing anything to set up a list. Since I very rarely use such searches, there isn't anything DDG could learn about me from avoiding just those searches going to DDG. OTOH, using site searches more frequently would be a win for privacy.