Dell vs Sun
Why anyone would go to Dell as a serious Datacenter solution is way beyond me. Sun sells damn good kit, but there's always that question in the back of your head... Of course, that wouldn't concern me, as everything is open. If Sun gets bought out, then I would still have support for the forseeable future. If Sun goes it alone, they'll be around for the next 5-10 years at least. If the impossible happens and Sun just disappears, then there will be someone to take up the mantel of supporting the "legacy" Sun gear. No real worries there.
Solaris is the only real OS that can take advantage of Nehalem, and Dell has no clue how to do anything useful above the low to midrange of the market... Of course, Dell supports Solaris now, so perhaps they will push that on their Nehalem boxes...
There are no real technical questions against the Sun solution. It is all just FUD.