If you're in the US, this weekend is Labor Day Weekend. For the non-US citizen, Labor Day Weekend is Summer's last stand. It's the last day when you can open a beer at 3PM and use the excuse, 'Hey, it's the summer! I'm allowed to.'
Whether you're celebrating Labor Day Weekend this weekend or not, be sure to take advantage of the last gasp of summer (unless of course you're in the Southern Hemisphere, in which case, go enjoy the start of it!). Sometime in October when you're mulling over the best way to phrase, 'Our results were not what we expected,' or some student brings you back a 2 week late homework and asks you if you can regrade his extra credit, you can at least think back and have a fond memory of the end of summer.
So unless you're defending on Monday (or Tuesday), don't think about your PhD this weekend. You'll have plenty of time for that in the coming months.