Decide for yourself:

Opera's techies downloaded the page using wget, in three different formats, identifying as Opera 7, MSIE and Netscape 7.01. The files sent to each browser are different, which is not necessarily suspicious, and the one sent to Opera7 has less content and is bigger than the one sent to IE. But that is not necessarily suspicious either.

Where it does get suspicious is when you look at the style sheets MSN sends to the browsers. The culprit, says Opera, is a 30 pixel value set on the margin property in the Opera style sheet. This instructs Opera to move list elements 30 pixels to the left of the parent, which means content moves off the side of its container, which means it looks like Opera is broken.

Opera tried to test whether or not this was deliberate by changing identification to the non-existent browser Oprah. This returns the IE style sheet, which works perfectly well in Opera. In Opera's view MSN is therefore looking specifically for "Opera" in the User-Agent string and sending it a broken style sheet. That, of course, could still be a mistake, as it's perfectly logical to send IE as the default if the browser can't be identified. But as there was no need for MSN to design an Opera-specific style sheet in the first place, one wonders...

Sounds kind of slimy to me. Go grab the whole story