I've just upgraded one site from 3.1 to 3.5 and I'm not sure at which version along the way the ModelAdmin search/filter form was moved from the left side to be opened by clicking an icon in the top right corner, which after the form appears on top of the page. I tried to search if there is an option to put it back the way it was before, but didn't find anything. I could also override some template files if I knew which one(s).
I think the new search form layout is good in cases where you rarely need the search (doesn't take up space), but my client told me that she uses the search all the time as she's managing over one hundred DataObjects in the list.
Thank you for your help! :)