I've written about it, and written about it, and written about it some more. A very large (70gb) object in the SharePoint recycle bin resembles a steel wool hairball — you know it's there, it hurts like crazy, and you just can't get rid of it. Microsoft gave me two choices…
I could wait for the WSS/MOSS Service Pack(s) 2, because they're supposed to fix the problem. Well, I tried to install them (on a test system, natch) but WSS SP2 ran for days (no kidding) before I finally gave up. Seems that the update just couldn't handle that big an item in the database. Maybe if you already have SP2 installed and THEN create and delete a hairball, it might work, but I'm not going to try it . Let me know how it goes.
The second choice was to restore the offending library, which contained one folder holding over 100,000 documents, and then delete each document manually, flushing the recycle bin(s) every few hundred documents. I can tell you from personal experience that this works, although the clerical folks who were drafted into doing this grunt work still won't speak to me and have all retired on disability with terminal carpal tunnel syndrome. If you want to try this at home, I suggest you select "Edit in datasheet view", which at least lets you select and delete a bunch of documents at one time. Also allow yourself plenty of time. Lots of time.
cwogle