Acer put all these options behind a remarkably simple interface, with large, can't-miss shortcuts for each installed program. Unfortunately, adding software to it required far more tinkering than most users would accept. It also failed to print anything, even though it claimed to recognize an HP printer/scanner.
Asus's version of Linux looks almost as simple but badly needs to be simplified once you get past the first layer of program shortcuts. And it wasn't much more hospitable to add-on programs.
Dell, by contrast, bundled Ubuntu Linux, a slightly more complicated but far more capable version of Linux that easily stands up to XP. If only the Mini didn't have such a wretched keyboard -- and a price inflated over the usual $349 by extras such as Bluetooth and a webcam, which should have been standard -- it would be easy to recommend.
What to get instead? If you're buying a netbook as your sole computer, knowing that you'll only use it on the Web, Acer offers the best bet for now. If, however, you're buying it as a third or fourth computer and are willing to tweak it to fit your own needs, look at the MSI.
But it might be better to wait. If these manufacturers have the good sense to steal each other's best ideas, we should see significantly better choices before long.