One Google account, many (and more) mail adresses

If you have a Google Account, it is likely to be something like myname@gmail.com.
From this simple GMail account, you can receive mails sent to numerous variations from this single name:

1. in the first part of the name ('myname' in our case), you can add any 'dot'. Thus, you could be reached at my.name@gmail.com but also at m.y.name@gmail.com. All your mails will be received in the same mailbox as myname@gmail.com; if you don't configure anything else, it will be completely transparent for you. So what is it for? The first time I came across this feature (http://bit.ly/VQZF5 through a @GuyKawasaki tweet), it was depicted as a nice way to "trick/fool" systems like Twitter so that you can open multiple accounts with a single mail account (which is far more convenient afterwards for reading the different mails)
2. at the end of the first part of the name (still 'myname'), you can add a '+' followed by any valid string of characters. Thus, you can have "myname+ServiceProviderOne@gmail.com" which will also be received at myname@gmail.com. You can use this naming pattern each time you subscribe to a service (Twitter, FB, ...). This is a very interesting way of keeping track of potential spammers...
3. last, you can either use @gmail.com or @googlemail.com: it is equal.

Then, you have that many different ways to decorate your single GMail account, without managing the hassle of multiple accounts.