We have all Dells at work, bought by me and a mate in 2 batches of 8 and 12. they are Dimention 8400s and are FAR better than anything else out there if you look at the costs involved.
If you look at the alternatives, you could buy from a "local" "PC maker", but these are just cobbled together from any old bits, any old case & not tested. or you cold buy from another "big name supplier" such as HP, Fujitsu-siemens or acer. These usually end up being much more expensive as the normal online price doesn't include a monitor. All of ours have 17" LCDs.
Another thing, ours have a similar "Big green" heatsink thing, but it's more than it seems, they use heat pipes which are typically used on SFF PCs as they work well and can be really quiet (as are ours)
To sum up, we have 8 + 12 identical PCs (which in its self is a big plus), that are quiet, reliable, fast and (overall) better and cheaper than anything else we could find.
Personally, I'd recommend them for business use.
As for home use, I'm not too sure, after building my last 6 systems, I'm not sure, though the XPS range looks good (not for sale in spain yet though).