I waited about a month and a half before installing win8 because i too didn't like the metro ui, compared to the start menu i had been used to since 1995. instead of a start button, you simple move your mouse to the bottom left corner and a tile appears to click on the start panel. I'm getting used to it, and deciding not to go back to win7.
Just with anything, when you introduce change, there will be people that simply won't like it. I was one of these at first.
If you're thinking of making the change, you should look at any devices you connect to your computer that are important (printer, scanner, webcam, etc...) and make sure they have software for win8 and your device.
If you're upgrading, you should make an image of your computer with a tool like Symantec's Ghost (or other imaging utilities). So that if you need to go back, you have a complete image of your system before the upgrade.