You can delete .DS_Store files with
OnyX. Get version 2.4.1; the next one is still in beta. After installing and launching OnyX, select the Maintenance tab and then click Rebuild (that's where to go for the Snow Leopard version but I assume that the Lion version is the same). After doing this, the folder positions will revert to defaults but you can re-arrange them to your satisfaction. That re-arrangement should stick.
Thanks for the pointers, but:
(1) I've learned that any assumption that 10.7.x and earlier versions of OS X have completely similar behaviors is not a good position to take and certainly not to implement.
(2) At the best of times I'm wary about third-party applications which could do something nasty to my OS/computer and would need iron-clad guarantees that they wouldn't.
(3) I have extreme reluctance (due to my major insecurities derived from recent experience) to do anything with or to my machine that I don't understand (at least in broad strokes).
