They sure have difference of opinion. Open source has been “evil” for Microsoft. Then they acknowledged that it was a problem for them. Now Steve Ballmer is on record saying :

Innovation is not something that is easy to do in the kind of distributed environment that the open-source/Linux world works in…our customers have seen a lot more innovation from us than they have seen from that community.

On the other hand, Sun Microsystems seems to have learnt few lessons. Paul Andrews informs that Sun and Oracle have thrown “their collective weight behind the inexpensive x86-based (Intel chip and clone) servers running Linux or Sun’s Unix-based Solaris”. He further adds:

Sun wants first of all to make sure it loses none of its well-heeled clients to IBM, a big Linux supporter, or to Dell Computer servers running the hated Microsoft Windows. Second, the alliance would like to lure as many Windows-based businesses to a Sun-Oracle solution as possible.

The alliance indeed seems formidable.