Thats mostly old news, linux has already pushed those servers out. But what is likely not told is that it is linux clusters that are doing the work, not a single box. While a single linux server may be faster than a sun box it cannot come close to handling the same number of simutanious users, hence the linux clusters.
Where MS has to watch out(well not much they can do about it) is the desktop. Within the next year expect to see a serious errosion of the MS base to linux. Check out this
http://www.desktoplinux.com/news/NS8523030175.html
Linspire is the old lindows. This is what is installed on the cheap linux boxes sold at wally-world and other places. Other desktop styled distros will soon include the client. This in turn will quickly cause the few remaining manufacturers to either write drivers or open their code to the open source community.
This is something that MS understands and is activly preparing for as they develop new models of revenue streams. Notice how they are making lots of noise lately about online applications. The other vendors you mention dont have all that much to worry about.
Oracle is one of the leading db and will continue to be a leader at the enterprise level, no open source app comes close. Even the free SAP software cant matrch Oracle and MySQL and Postgress will never manage to touch Oracles base.
Cisco will never lose their grip on routers and appliances, while a linux box can be used to duplicate what Cisco does a linux box will never make it for the backbone or major ISP level, again it comes down to scalability. A linux box is fine to plug a T1 into and route but it chokes on a DS3 so it will never make it to a OC48.
Sun OTOH is and has been in serious trouble for a number of years. Only its past domminence and installed customer base is keeping it afloat. Their attempt to gain with solaris has been seen as a joke within the linux community. No one want to run it even if its free.