For PSEWHacking there is an IconService which serves PIMO and Application icons.

"Quick" start:

• The icon service is available if the two bundles org.semanticdesktop.nepomuk.psew.pimo, org.semanticdesktop.nepomuk.psew.pimo.bundle are started.
• The main way to access the service is as an OSGI service, the service is org.semanticdesktop.nepomuk.comp.iconservice.bundle.IconService.java, and you get it from the OSGI service registry (i.e. not middleware, just normal osgi)
• The service has two methods: getPimoIcon and getAppIcon.
  • Pimo icon takes a URI, giving you the icon of the class or instance, the current pimo icons are shown here: http://www.semikolon.co.uk/blog/images/all.png
  • App icon is one of the constants listed in de.opendfki.pimoeditor.vocabulary.PimoIcons? (from the org.semanticdesktop.nepomuk.comp.iconservice bundle, yes the name is bad) and also listed here: http://www.dfki.uni-kl.de/~grimnes/2007/12/pimoeditorIcons/etiquette/
  • Each method also takes the size of the icon to serve, the icons come in sizes 16x16, 32x32, 64x64 and 128x128.

If you care about the details:

• There are two bundles because one contains the icons+a servlet to serve them, the other wraps this up as an osgi service, serving icons as jface-resources.
• The icons are initially svg, these are also in the bundle (I think :), but are not served anywhere :)
• The icons were automatically converted from svg to PNGs, this means the 16x16 icons are quite fuzzy.