It’s likely that Apple was working on this update even before Lion’s initial availability, which means that much of 10.7.1’s improvements is stuff that Apple already knew about. And that means that bugs that were found after Lion’s release could still be present– but I’d expect a lot of them to be fixed in 10.7.2.
If you’re on 10.7, Step One is be absolutely positive that you have a current backup. You can go to Time Machine’s menu and tell it to “Back Up Now” (that’s what I did). Step Two is get 10.7.1 via Software Update under the Apple menu. Step Three is restart, which the Installer will insist upon. You might get some disk activity and fan noise immediately after the restart, but it ought to go away in time. You can restart again after that and from then on it ought to be smooth sailing.
You can probably tell that I am not keen on Lion. I prefer Snow Leopard for several reasons, some of which I will write about someday soon. But, if you’re already on Lion, you’ll be happier after installing the 10.7.1 update. Just be sure you have that backup, just in case.