With a short handlebars your hands are only very slightly further forward than the plastic handle. I use a short flansberrium style one and I love it, mostly because it is much more comfortable to grip since the hand can actually wrap around it. The brake is also much more ergonomic to use.
The other advantage is a bit more leverage, slight disadvantage is that the seat moves further behind you when you pull on your handlebars.
I think the plastic handle is still most common among muni riders, but short handlebars are quickly gaining popularity.