The Explorer process runs a lot of important things in Windows, and when it crashes, it can really slow you down. It turns out, however, that you can sandbox Explorer windows so if one crashes, it doesn't drag your whole system down.
One option in Windows Explorer that I find extremely useful is the option to separate out the taskbar and desktop from the other open Explorer windows in two different explorer.exe processes. This makes sure that the taskbar and desktop stay alive if explorer.exe happens to crash, which it does quite often in my experience.
This is especially useful in computers that are used by not so computer savvy people, who won't know to hit Ctrl+Shift+Esc and run explorer again in case of a crash. I find it a timesaver too, because I experience lots of crashes when exploring my phone memory in Explorer via Bluetooth.
In Windows 7, there is a straightforward option in Windows Explorer under Tools > Folder Options > View > Launch Folder Windows in a Separate Process (Not to be confused with "Open Each Folder in a Different Window" under the General tab).
In Windows XP and before, a registry hack will do the same thing. Open up Regedit and go to HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionExplorer, right-click in the right pane and create a new DWORD called DesktopProcess with value 1.
Note that sandboxing this process will be a bit more resource intensive than keeping them as one process. However, if you've got fairly recent hardware, this'll probably be a welcome change. Now, if and when Explorer crashes, you'll only lose that window and not your entire desktop.