On the desktop site you'll see a bunch of little symbols on the right of the share box. Click on the link symbol and you'll get a new box. You can paste into that one. (Tested on 3.2 just now - can't verify for earlier versions)
Great. The only way I was able to get it to work was in Firefox, but it seems like Firefox looks like crap on the Xoom compared to the built in browser. Did you have to change the UAS setting at all or does it finally default to the desktop site instead of mobile? I tried it on 3.1 and when you hold to paste all it will do is select the text box (turns blue) and doesn't give you the prompt to paste. Sounds like that has been fixed.
I tried it from the app. I can post a link but it doesn't post the summary and a thumbnail like if you post it from the full blown website.
Thanks for the help. Now I just need to wait to get the 3.2 update....