Maybe I agree with facepalm. But also with informatimago down at the bottom. It's probably be in my best interest to read most unix commands straight from man.

I tend to use tar -czf <file> to untar. If it didn't work I'd proceed to tar -xzf <file> or tar xzf <file>. Even so sometime my machine wouldn't accept the command until I tried something like untar (not real!) or unzip or gzip. But those were mostly out of frustration.