Yeah, back in flight school there were signs all over the place reading "DID YOU CLOSE YOUR FLIGHT PLAN?!?!?". On the plane signout sheet, the breakroom wall, the locker room, the bathroom...everywhere you could think of. I always wrote it on the bottom of my navlog as if it were another leg on the flight. I always managed to remember, but some others didn't...I don't remember them ever getting fined by the FAA though.
I'm a readback champion, so I like IFR plans out of places with grumpy, pissy controllers. They will never of course give you the route you filed for, but instead some horribly tedious readback which has you departing in as close to 180 degrees from your eventual enroute airway as possible. They read it to you in the cockpit like that speed reading guy who used to do commercials for FEDEX. They figure that might be enough to rattle you into departing VFR and filing from the air I guess. Nothing lets the wind out of their sails than a perfect readback in a single pilot plane. A readback that has more goofy headings, intersections, altitudes, and such.
The funny part is then once you leave tower, and check in with departure, they route you direct anyway? Why they play such games with people I have no idea?