At this moment the extract and add icons in Xarchiver looks really uggly. and since i can see that Xarchiver have a tango icon, i would beleve that xarchiver would want tango styled extract & add icons wich file-roller do have. I will upload the icons on this bug report.
Created attachment 1334 [16x16] add-files-to-archive.png
Created attachment 1335 [16x16] add-folder-to-archive.png
Created attachment 1336 [16x16] extract-archive.png
Created attachment 1337 [24x24] add-files-to-archive.png
Created attachment 1338 [24x24] add-folder-to-archive.png
Created attachment 1339 [24x24] extract-archive.png
THe svn version already has tango icons. Look at this screenshot: http://xarchiver.xfce.org/screenshots/xarchiver-0.5.png The toolbar icons are those from Tango.