[John B kindly pointed me at this thread]
Apropos Portfolio, it definitely offers multi-user support with searchability through either the Portfolio client application or a web interface (Portfolio NetPublish). The latter is read-only. Portfolio is positioned as a DAM tool and as such has no 'lite' image editing tools as some apps have. Whether this is good or bad varies with the user's preferences. In short, Portfolio assumes you'll be using the likes of all/part of Adobe CS so doesn't try to compete with those more powerful tools. There's more over at PortfolioFAQ.com.
Part of Portfolio Server is an optional module called ProjectSync. This is the first significant use of Adobe's Version Cue CS3 plug-in technology. With ProjectSync, instead of using VC's own database, a VC project using ProjectSync harnesses Portfolio in the background. This allows you the richness of Portfolio's many fields for searching, from within CS3 apps like Bridge. In this scenario Bridge also reads thumbnails in from Portfolio rather than creating thumbs on the fly, increasing Bridge's performance.
As a buyer, do be wary of simple comparisons. Most DAM products have some (often small but) significant differences making simple bullet-point comparisons less than helpful. You want to look for best fit you your workflow. As a Portfolio consultant [sic] I'm arguably not an impartial advisor, but I can say that Portfolio certainly is a happy choice for plenty of multi-seat users and is showing growth at present. The app is the oldest DAM program (its roots go back to 1994) around - though it's been re-written since then (!) and is still being developed. A look at Extensis' new Suitcase server tech gives a glimpse of where Portfolio's probably headed in tech roadmap terms. In buying into a multi-seat solution, the comparative cost (vs. single seat apps) does mean you want to check you're not the only user (often the case with CMSs) and that the app will be around for the time you're likely to be using it!
Note: Portfolio v8.5.1 is just released for both OSs and all app components. See http://www.portfoliofaq.com/forum/viewtopic.php?t=1491
I hope this helps...
Mark Anderson. www.portfoliofaq.com