I am extremely selective in the previews that I have Aperture generate. For the most part it consists of my top rated images and maybe some other stuff that I use regularly. If you have read some of my work-flow posts or file management eBooks you should know how to control Aperture previews in a lot of different ways. I thought I would share something that I found obvious but surprised a friend of mine the other day when he saw me doing it.
The first thing is that you can use Aperture itself as a media browser for any application that accepts images as drop items. If Aperture has a preview generated - that is what you will get. You can use all of the search functionality and it can sometimes be easier than using the media browser window itself. If you have started to fine tune your preview generation then you might want a couple of ways in Aperture to make sure you are only looking at images that actually have a preview. Since I generate previews for my top rated images I just use that in addition to other search criteria. In some other cases I have an album called previews existing in a project that I use to house images that have previews - that is how I generated them in the first place. I also typically have a smart album for every project that lists top rated images for a lot of purposes. It serves double duty when I am using Aperture as a media browser.
Here is another tip that might surprise you if you haven't tried it. The media browser that is opened for ANY application works with any other application. It even works if that target application is not "media browser enabled". What I mean is you can open a media browser for an email message and drop images from it just about anywhere. You can drop them on the desktop, heck you can even drop them in Blurb's BookSmart book software and bypass that horrible UI for browsing images that is included. Try it, you'll like it.