I've learned a ton about color correction/film response simulation and lens blur/bloom/bokeh simulation
For more detail on a project of mine that involved it you can go here:

Link: helios.mine.nu --- Lens Simulation

I also did a bunch of research into simulating auto-exposure

Link: www.maxwellrender.com

With Maxwell Renders SimuLens tool you can (on any HDR image you feed it) produce a very realistic lens simulation, simulating the aperture and any dirt/obstruction on the lens:

The above was rendered in Vray by me, then color treated and given to Maxwell for the lens effect
You cannot (as far as I see) do your typical cheesy lens flare with the several concentric rings

Some tests of throwing it some brush strokes done in photoshop in 32bit:




Not quite realistic, but adds a nice touch