This is the filament driver I used (together with my hobbed bolt) sucessfully on my Ultimaker for the last 10 months (and this is PLA!)
It was designed originally for 3 mm but it would work alike with 1.75 mm as it boils down to how to the hobbed bolt (I ran it successfully with ~2 mm trimmer line filament)
This thing is in progress, though it is currently revision 5.3: I just should stop spending days on it since it is extremely reliable (much more than what I had stock).
It is written with openscad and it is fully parametric (incuding height, average thickness, bearing diameters...). It also prints quickly (2-3 hours), and almost in one piece (2mm walls and 30% infill is enough as it features internal dedicated structures).
People may be interested in the unusual features I think it has. Check my blog for the details.
Update: scad file 5.3b fixes the main body height that was 2mm too small for the hinge screw (and idler M8 screw).
Update the "simpleclamp_xxx" files are useful in case you want to use a blind rivet nut (recommended) or a push fit to hold your bowden tube, check the appropriate file name (else unneeded).
Check the detailed instructions on my blog here http://betterprinter.blogspot.fr/2013/04/rollerstruder-filament-feeder-driver.html
The bowden tube clamp derives from the ingenious Owen's design, which itself uses Aubenc's Knurled surface finish and screw libraries. Expect these to be dropped in the next revision though, because I will favor a simpler and more compact bowden clamp thing.
Crappy and useless video here with 3mm wood filament: http://www.youtube.com/watch?v=oWVvKtcfUrI and 2.4mm crappy trimmer line http://www.youtube.com/watch?v=VQk3jsIkmz0