I considered singlespeed for a while as a commuter and I had a singlespeed bike I really liked to ride but it wasn't really a good bike for commuting. Ultimately I decided gears came in handy with a bike loaded down with fenders, racks, stuff, lights etc and the occasions I pull my trailer its nice to have the lower gearing. Other cases when having gears is good is when its windy. Its not that hilly here and I could go the singlespeed route, but for now I'll take the gears.

Singlespeeds are a blast to ride around though and would be an awesome no frills commuter. If you want to try making the switch purchase a much cheaper singlespeed road bike and give it a whirl.

Adding on to the previous post if you wanted to go cheap you could throw dropbars on your hybrid which would make you more aero and also make it a singlespeed. Doing this might cost a bit of cash, but you might end up with a killer singlespeed cross bike when you are all said and done.