I have been using the "paste from word" icon for the past two weeks in WordPress 2.5.1 because I write my posts in a word processor offline and paste them in later - this new device seemed quicker than using my usual word processor and then stripping out all the unwanted formatting code in the HTML editor.
I use Firefox as my internet browser, so I was unaware of a problem until notified by a couple of subscribers: since switching to the "easier" "paste from windows" button in WP 2.5.1, many of my subscribers had not been getting text with their feeds - just the post title - and if they clicked through to the site and if their browser is Internet Explorer, they got the same thing: Blog title, post title, no text.
It turns out this "paste from windows" system was inserting script in front of the posts that halted further printing of the material. I had to go back through all the posts for the past two weeks and strip it out. Once that was done, the site worked normally on IE again, and my subscribers tell me their feeds are normal also.
I now use my original system of writing in another word processor (Star Office), but then I copy and paste to notepad and then back to Word Press.
Just a heads up.