At risk of letting my psych background get the better of me, for those considering the pros/cons of implementing basic file icons, there's a lot of evidence to support their use in UI design (mainly dealing with processing mechanisms relating to iconic memory & a few other areas of concern). In short, they can increase one's ability to differentiate between given items faster without the need to dip into the bag of tricks behind language processing. Won't comment on the extent of any impacts for a programming environment (if you're using the sidebar vs cmd+p chances are you're hunting for something, not to mention that the individual files kind of matter -- so it's not so much sorting them out as it is just grouping stuff mentally at the macro level).
Assuming that we're simply looking at an extension of the sidebar API, it wouldn't be a big deal if you want them or you don't. Everybody wins
. Sorry about the tangent.