Lastpass, being primarily a browser plugin, makes generated passwords much more convenient. When I'm setting up a new account, I press Alt-G to bring up the generator dialog, and then it auto-fills when I need to log in. I honestly don't know most of my passwords (I still memorise my primary email password, so I'm not totally stuck if I lost access to LastPass).
This is a compromise, because I'd prefer to trust an open source tool and an encrypted local file, but I trust Lastpass enough, and the convenience is very nice.
There's addons for Firefox (KeeFox) and Chrome (ChromeIPass), making the UX of KeePass pretty much the same as of LastPass. I've switched about a month ago and am happy.
This is a compromise, because I'd prefer to trust an open source tool and an encrypted local file, but I trust Lastpass enough, and the convenience is very nice.