Ars Technica's belief is that FireFox's success will undermine Opera's case somewhat- but the case seems to go beyond merely bundling IE, but the inability to remove IE should you wish to, and the well-known MS attitudes to international standards.
Flies and Bikes Blog
Opera v Microsoft in EU
Opera tries to force IE into W3C compliance with EU complaint; Firefox's success may work against it (report at ArsTechnica) - The internet browser company Opera has filed an antitrust action against Microsoft. The complaint is about the bundling of Internet Explorer in Windows and the alleged breakage of international web standards. There's another analysis over at Groklaw, of the usual high standard.