Yes, you can easily dual boot between Linux and Windows 7. The wubi installer automatically makes its own partition for Linux, and if Windows crashes it will save your life. When thinking about Linux you must think about which OS you're comparing to Windows 7. Ubuntu 10.10, the newest version of Ubuntu, which to my knowledge is the only Linux OS with a netbook version, is incredibly fast but takes a lot of getting used to, and the version has countless glitches. Ubuntu 10.04 is probably the best choice. For a desktop, you can also get Linux Mint which is very similar to Ubuntu but with a different theme.
Linux will NEVER get a virus. It will never shut down on you, either. The interface on any desktop edition is very similar to that of Windows, so there's not much new stuff to learn. Linux also has a wide variety of software and a software store, and by "store" I should mean "installer" because everything is free. There's also emulators which will make certain Windows applications work on Linux such as Call of Duty Black Ops or Photoshop CS4. The speed of it, though, technically depends on your machine and also how much you've infected your Windows 7 partition. Even still there's not too noticeable a difference. It'd be a real difference if you were running Windows XP or Vista, but not Windows 7. Windows 7 is also very automated and Linux is very manual. The best way to describe this is connecting to wi-fi. Every Windows 7 machine comes with pre-installed drivers for wireless and comes with configuration, with Linux you have to install your drivers for it to work. The only really automated thing about Linux is installing fonts and how many things come pre-installed (such as Firefox or a torrent client). It's not really more intelligent than Windows, it's just a slightly different experience, more so with a netbook edition, and even so eventually won't feel much different. The only huge difference is that everything is free, even screen recorders and video editors. It's also very organized, and is a good thing to have should Windows ever crash. But it makes for many limitations if you're thinking about a permanent switch.