You can get to it at http://www.webpagetest.org/
It has a fair amount of capacity (can run 6 tests concurrently) so as long as nobody posts it on slashdot or digg it should be in good shape and be able to handle any testing needs. For those of you not on the east coast of the US it also gives you an easy way to do remote testing to see how your page loads from here.
The online version is actually a lot more convenient than the installed version because it takes care of clearing the cache for you, running multiple tests and has all of the results already saved out in a way that's easy to pass around (either by url or by shipping the actual images around). It also makes available everything the desktop version has (waterfalls, optimization checklists, optimization reports) and also includes a screen shot of what the browser looked like at the end so you can make sure the page you measured was actually what you meant to.
Here a gratuitous (albeit small) sample of the waterfall:
