Although my bathroom is pretty much done, I made a few simple upgrades recently that had a big impact on the usability of the bathroom for me.
First up was the toilet seat. My old toilet seat was a bit on the junky side and one of the plastic washers that helped keep it in place had developed a crack. As a result the seat would wobble a little bit every time that I would sit down on it. Even though it wasn't the end of the world it sure was really annoying. 
I thought about just replacing the broken plastic washer, but then I found a nice inexpensive toilet seat at Lowe's that sure beat out my old cheap plastic one so I decided to replace it. The new seat is molded wood in white with chrome mounting hardware. It is definitely a much needed upgrade.
Replacing the toilet seat took just about five minutes. I removed the old seat, screwed on the hardware, put the seat in place and then tightened everything down. I can't believe I hadn't done this earlier. No more wobbles for me!
In addition to taking care of my toilet seat problem, I also found a solution for my toilet paper. There isn't much space on the wall around the toilet for a wall mounted toilet paper holder due to the door and my built in cabinet. On top of that I didn't want to put mounting holes in the bead board on my bathroom walls. As a result I've gone without a toilet paper holder and just set a roll on the top of the tank until now.
On a recent trip to HomeGoods I spotted an inexpensive chrome toilet paper holder that was free standing. The look matched well with the other chrome hardware in my bathroom so I brought it home to try it out. Because it is free standing I can angle it and it fits perfectly next to the toilet. Toilet paper holder problem solved!
Have you done any small upgrades around your home recently? What little things have you done that made a big impact for you?