Every now and then, you may come across an archive that, when decompressed, creates tons of files in your current working directory. While most tarballs aren't created this way, it's been known to happen. If you want to verify that your particular tarball was put together correctly and creates a main directory to hold the sources, you can view its contents by typing:

$ tar tzvf archivename.tar.gz | more

(t is for a text listing of the archive. No extraction occurs.)

If there is no common directory listed on the left-hand side of the archive listing, you'll want to create a new directory, move the tarball inside it, enter the directory, and only then extract the tarball. Otherwise, you'll be in for a mess!