Like many IT contractors I have used good old Jobserve many-a-time over the years, enjoying its simple but effective interface and layout.
One of the main things that I liked about it was the speed at which you could set your criteria and fire off a search. It was literally: type search term -> hit enter. This would then search ALL jobs in ALL industries (that Jobserve catered for, of course). Recently however they changed the user interface (UI) which in my opinion has spoiled the user experience (UX) (note diligent use of acronyms 
).
“Si fractum non sit, noli id reficere”.
Now what happens when I go to search in the same manner that I used to, is that the page submits (looking like it is conducting a search) then reloads after hitting the server and tells me that I must select an industry. Err, ok (a bit of client-side validation would’ve been a nice way to save this uneccessary wait…). So I select the dropdown and, unusually contained within the dropdown, I see a list of checkboxes. Right, I think to myself that I don’t really mind what industry/sector I’m working in, in fact I quite like the working in different types of environment, so I just want to select them all. Oh, wait, there’s no select all checkbox, so I can’t.
So it seems that the only way I can ensure that I’m not missing out on a term-hit for any job across all industries is to check all 17 checkboxes contained within the dropdown (which I feel itself is a bit alien and not very user-friendly). That plus clicking the dropdown amounts to 18 MORE clicks than I had to do previously to conduct the same search across the same job sectors.
I’m not normally the type to bemoan something as trivial as a negative UI change but it is slightly shocking that a site/application the size of Jobserve (who have over 5.5 million unique visitors a month and sponsor Colchester United) let such a sizeable usability mistake slip past the user acceptance (UA) testing phase; if there was one that is. More importantly, it is annoying for me! (and most probably a lot of other users).
If that many users did the same search as described above, that’d be an extra 90 million or so uneccessary clicks per month. Thus I think it is safe to say that this constitutes a prime example of a UI and UX change mistake.
Lastly, and as an aside, on firefox (i haven’t checked in any other browsers) when the page is loading you get an awkward-looking multiple-select box which displays and then transforms and springs into a dropdown with the checkboxes inside, momentarily throwing the form all over the place. It just looks wrong.
For reference, here’s the old main Jobserve search interface:
http://replay.waybackmachine.org/20090205112807/http://www.jobserve.us/homepage.aspx