As I have said before I am a Windows guy. I have played with Linux off and on since kernal 0.98 but don't use it daily, or even weekly.
I have found the Mandrake/Mandriva/whatever it is now core, and Ubuntu easy to set up and use for email, word processing, spreadsheets, powerpoint, photoediting and management, listening to music, web browsing, file browsing, CD and DVD listening/watching/burning and to some extent-database management.
Other distros can generally do all of these things too, I just haven't spent much time with them.
Things they all seem to be able to do, but which always require a bit of fiddling is accessing Apple or Microsoft centric networks, network printers and so on. The Linux droids will pop in here and say how easy it is, but for those of us who don't live this software I stand by my observations.
I general I have found Linux better for supporting older printers, scanners and many other hardware peripherals. Assuming that it is a product that was widely commercially successful, or was the pet rock of some Linux nerd at one time. Windows and the manufacturers tend to drop support for older products like hot rocks.
I am not trying for $2000 so I haven't gone back and checked your needs list. If it stopped above this line you just haven't tried Linux very hard. But I suspect that like me your list has things below this line.
Where all distros fail is in the applications I need and use. KiCAD and GnuCAD and the like can be used, but are not nearly as good as the fourth or fifth best Windows application. There are several other packages I use that have the same problems. I don't use it but assume the same is true for mechanical design software.