We're considering starting the herculean task of tagging our library of photographs used in marketing - some 10k images.
In my research we wanted a solution that would have allowed cross platform tagging. The benefit being that any staff at a later point can, from anywhere in the enterprise, search for photographic material to use when putting together their own materials - or just for some stock shots for lessons etc.
I have thus settled on Picasa from Google. Mainly since this will run on both Mac and PC (only recently admittedly.) This is one up on iPhoto, for obvious reasons. Again though by moving off the mac we're giving up some ease of use. Trust me - go compare taggin photos in Picasa (full free form tagging) to iPhoto (you can do it all point and click)
The benefit to point and click tagging in iPhoto is that we could prescribe what tags would be available to whomever we employ to torture their soul by tagging and tagging and tagging and tagging and tagging and tagging. Whereas in Picasa the pour sap has to type any and every tag they wanna apply, complete with typos. Not only that we'll be leaving the judgement of the tags to a third party.
What I did find wonderful, and daunting, during this research is that all the iSstockphotos we've been buying over the past few years come complete with tags, lots of tags. It really brought home to me how well indexed and tag'd to the infinite power our images should be! Dozens and dozens of tags - pour sap!
If anyone has any suggestions on how to make this process less painful, even if someone could suggest how much the mechanical turk would cost for this task - lemme know.
My final descovery during this odyssey was how well thought out Google software can be. I've been working remotely recently, and I logged into my machine this morning via the VPN and set about installing Picasa for my research. Once installed it launched, but presented me with this brilliant dialogue...

Isn't that genius!