Well, I'm predominately interested in: WindowBlinds, ObjectBar, DesktopX, IconPackager, WinStyles and in that order. While Object Desktop has other applications, those seem to one extent or another to be the "anchor" apps for Object Desktop.
I first came across OD when, after messing around with Linux and the various KDE themes, I poked around the net to see if something similar existed for Windows (beyond just color schemes). I bought WindowBlinds first since it seemed a pretty good deal. After that you held out the OD carrot in the form of IconPackager and DesktopX

At that point I said, what the heck, might as well go hog wild, though I was a bit leery at first until I became more familiar with Stardock.
I was initially intrigued by the other apps included in OD, but once I purchased it, I found that I didn't need all the other apps that initially seemed interesting. At this stage of the game, I look at what I use from OD as primarily eye candy. I'll occasionally play with DesktopX. I use ObjectBar alot more, but not as much as I use WinStep. Sorry but the menuing in Objectbar to be not as flexible for my own purposes. I pretty much use it to get the XP task bar and start menu, but I find this to be not a must-have. That said, I've been using ObjectBar alot more than I have in the past.
While I could easily get by with WB, I look at an OD subscription as sort of having a stake in Stardock. Just because I don't use all the apps, or only occasionally, doesn't mean I don't enjoy playing with them. And eventually I may use them more and more as more features are added, or I find new ways to use them that weren't initially obvious to me.