I experienced a major crash in linux while online. Gnome crashed, I got a dialog box that explained what happend, I clicked ok and everything closed and sent me back to the login screen. I thought that it was very strange exiting my user account and going to the login screen. Is that normal to exit all the way to the login screen?

depends what crashed, the main point is that it didnt require a system reboot and it didnt effect other services like ssh or whatever you happend to have running in the background.

Like you pretty much stated, it wasn't Linux that crashed, it was Gnome or maybe X even that you were using. Linux crashing would have brought your whole machine down most likely with it, not just a login prompt to start all over.

Check your logs, they might tell you something that could have caused it.. etc.

Most program crashes just drag down the program, but in cases like that, it's better to be able to login again than to reboot or risk the entire OS. One minor bonus you have over most OS's/software is that if you can repeat what you were doing, you can send an extremely detailed bug report (or if your logs are clear enough on this, send your present logs), and it will probably be handled fairly quickly.

Problems like that are often the error of a programmer. Sometimes pointers get "lost", meaning they send data to places it shouldn't be, or accept data from places they shouldn't. Linux/XFree86/Gnome are pretty good at handling this, but no program is perfect. On the other hand, you're not going through a reboot/reinstall/scandisk, either.