From an article at www.makeuseof.com:
Just about when I thought I got everything out of Gmail, I discovered my top favorite feature. We have published over 30 tools in Gmail RoundUp 1 and almost 80 tools and tips in Gmail RoundUp 2 but never mentioned anything similar to this one. Tribute for this one goes to my ‘I am not into computers‘ type girlfriend.
Let’s say that your email address is ‘GeorgeBush@gmail.com’, basically everything sent to any of the following email addresses will be forwarded to your primary email.
And that’s not all, you can place as many dots as you want, it can be even something like ‘G.e.o.r.g.e.B.firstname.lastname@example.org’ and you’ll still get it on ‘GeorgeBush@gmail.com’
Additionally, I just also found out that you can embed random text to your email ID using ‘+’ sign. That is to say ‘GeorgeBushemail@example.com’ can be used as your email address, as well.