One of the features introduced with Aperture 3 that I pretty much ignored was flags and labels. I ignored them because I've been there and done that with a pile of other software since the beginning of time. Not that there is anything inherently bad or wrong with these two devices, it's just that I developed better ways of doing things since I started using Aperture - way way back in ancient times. By and large I "flag" and "label" things in my work-flow by grouping them together in albums that represent anything I want them to represent depending on the project - and I name the album appropriately.
I still think for a lot of things that albums are a better way of organizing your work-flow than flags and labels. At least they are in my work-flow. I have been living without them for years and never really looked back. So when Aperture 3 came along introducing flags and labels I took an attitude that they were included for all the "old fashioned dunderheads" that couldn't wrap their heads around a new and better way of keeping track of what they were doing. In other words a concession made by the Apple guys to those coming from other software that happened to have them - at least until those new users "got it".
Well after living with Aperture 3 for months and months I was determined to figure out how to integrate flags and labels into my new way of doing business in some meaningful way. A lot of my work-flows have some similarities across projects but that is where it ends - I have no absolute fixed way of going about things and my projects are diverse enough where color labels HAD to mean different things for different projects way back when that was what I used. On top of that flags are only good for "state change" type of things - in other words images that are either in one state or in another - not in two or more states of being. Flags to me have never been more than a really really simple bookmark that has meaning for one particular session - never some global meaningfulness.
So while I still believe albums are a better way of going about organizing your photographic life for the most part - I have integrated labels and flags back into my toolbox in Aperture 3. I won't go into a specific prescription as I don't believe that is all that valuable - everyones needs and way of doing business is different enough to invalidate a lot of specifics. If it's not and your organization already has a label prescription - you know what it is and you are set. Instead I will give you an overview of my findings with some general advice if you are still thinking about where labels and flags fit into your overall photographic life.
Let's start with color labels. For the way I work and I would imagine everyone else out there - for labels to be useful at all they absolutely must have a global meaning of one and only one thing across all projects - if they don't the mental gymnastics of trying to figure out what they did mean for one project or another or one image or another is worse than not using them at all. If you do have things in your photographic life where you need a quick visual reference of a few particular things across all of your projects and images color labels can be very effective - the least of which is in the context of an active project. Where they really shine is in more global searches of your library where there is no project or album context. Personally I don't use them to reflect things I already know from other metadata activities like ratings, keywords, etc. I definitely do not use them to reflect on things like "done-ness" or "selects" I find that redundant and to honest counter productive.
Moving on to flags - I still find these the most useful to temporarily mean whatever I need them to mean in the context of whatever I am doing right now, not some global static one meaningfulness for all time - that is what I use color labels for. For example - if I do a quick search in a project or a folder of projects for some broad category of thing I want to see and then need to mark a few specific images while viewing that search and retain the ability to quickly see just those images when in another context. When looking at a smart album I will flag a few images and jump to the containing project for an image and do a search just on flagged images. Things like that.
My really big complaint is that Aperture 3 doesn't embed flags and color labels in IPTC as other apps do. If it did color labels would be a very effective tool for cross application work-flow. What do you guys use flags and labels for?