This is in response to Russell's origional post
My single sentence response: "Let the developers know how they could make their software better for you."
Obviously patches are best, but a well-written bug report or feature request is taken by most projects very seriously (The only notable exceptions for me have been anything by DJB, and MythTV).
"Make it more like Photoshop" is not a good bug report or
My next thing would be to request more docs. I think the Inkscape project have done very well with this over the last few months, they now have a huge amount of great tutorials. If telling someone what you've achieved with FOSS results in a "cool" or "how'd you do that" write it up!
One of my own personal gripes is bad Windows ports of FOSS, for a few apps (including Inkscape itself) I've contributed small patches to make them better citizens on Windows.