Let's start with the one and only trackpad gesture to trigger LaunchPad. It's a four-fingered pinch. Up pops a iOS-looking grid with all your apps' icons. From here one can click something to launch it or move stuff around and categorize icons by putting them in folders. A click anywhere else that's not an icon will take you out of the LaunchPad, or you can reverse the gesture by spreading your fingers outward on the trackpad.
Now, the gesture itself might sound ridiculous in that it seems to require the utmost focus and human talent to execute, but it's easy as pie. Seriously. Only occasionally do I have to attempt the gesture twice to activate it. So, for those complaining. Just stop. By the way, you can setup a keyboard shortcut if you want. Just go to the keyboard preferences—it's the first option. And later on, I'm sure there will be some more options for LaunchPad, either by Apple or a third party.
Next, let's talk about these people with gobs and gobs of apps. Because some people have so many apps, they say LaunchPad is useless and confusing while having to sift through pages and pages of icons. Spotlight, they cite, is better at launching apps. It's true that Spotlight is a great tool for quickly launching apps, but it does require a click of that little magnifying glass in the corner and then a few pecks at the keyboard. If you're anything like me, I automatically reach two hands to the keyboard in search of those home keys every time I type something, all which takes time. But it's not all about the time it takes to launch apps either. The UI for LaunchPad is downright pretty. For novice users new to the Mac, I'm almost certain a large percentage of them would prefer the LaunchPad to almost anything else.
To those power users with a kazillion apps, let me suggest this. Organize only one page of icons to your liking, starting with only 10 to 15 apps. Don't' worry about throwing icons into folders and categorizing stuff and making a page full of folders all filled with crap. Let those bright and shiny 15 apps on your "home screen" be the category of "Most Used." There you go—LaunchPad is now cleaner and more useful. Let Spotlight or Quicksilver or whatever handle everything else.
Also, I don't know if you've actually used any of the fullscreen apps yet, but having to mouse-up for the menubar can be a pain, and that's just another step for you Spotlight launchers out there. In that situation, a four-finger pinch on the trackpad, and voila! Everything is at your fingertips.