Something all Aperture 3 users might not have noticed is the ability to select multiple objects in the project inspector. I don't recall exactly when this was introduced – I believe it was with Aperture 3 – but it's been a god send in reorganizing my library on the fly. As with all applications and all other data objects the usual click to select, shift click, and command click perform as expected.
Last time I mentioned that I create albums for every image grouping I ever take time to make in the first place. At the point the number of albums within a particular project becomes unwieldy I typically create folders that subdivide all those albums into folders based on the nature and purpose of those albums in question. One of the projects I shot for Mirror-Mirror isn't crazy yet but as you can see at the top there are quite a few albums already.
Above I selected a bunch of albums that represent a a few on-import VSCO preset treatments that were applied while I was on the road. To tidy the project internals a bit I just selected them and dragged them into a new folder. As you can see I already had a folder full of slideshow variations that I don't frequently visit inside Aperture 3.
One last note on this quick Aperture 3 tip. True to the anything anywhere, in any order nature of Aperture no matter how many things are selected in the project inspector and no matter what projects those things live in, using image search will show results limited to the images contained in the selection. Pretty cool huh?.