lens choice: 20mm f1.7 or 25mm f1.4. ?

Not a hard and fast rule or anything, but in my opinion the FOV and size of the 20mm are well suited to landscapes or street type stuff, while the 25mm is a little more flattering for closer portraits and the bokeh / blur with the f/1.4 aperture is more pleasing in some situations.  The slightly longer focal length means that distant objects are larger, and thus more 'blurred' at f/1.4.

I own both, and if I'm shooting people I'll always take the 25mm.  I grab the 20mm when I want a compact lens for travel...  Can't really justify both, but I can't seem to part with the 20mm - got it with the GF1 and just can't bring myself to sell it!

When i only had the 20mm I loved the people shots I got with it, but now that I own the 25mm I never use the 20mm that way anymore due to the increased distortion.  I usually carry the 14mm / 25mm combo rather than bringing the 20mm.  Both are good lenses though, can't go wrong with either if you have a 45mm or something for portraits.