If you already have a system running Windows 7, especially if you have a high-end computer, I don't recommend upgrading to Windows 8, simply because the cost doesn't justify the changes. If you come from Vista or XP, I'd say take Win8 over Win7.
I've been using Windows 7 since it came out and tried Windows 8 halfway 2013 to see why people hated it so much.
My first impressions were ... WHY does everybody hate this??? It already started with the installation. With 7 I installed the OS, then all the separate drivers, then did all the windows updates, all the software, and it took me the better part of a working day to get everything up and running. Windows 8 cut that time to 2/3 of the time.
The after everything was properly installed (on an old computer), I noticed that the startup times were very impressive. I was up and running while Windows 7 still hadn't shown me a login screen...
Win8 looks and feels a little bit different, but hey, Win7 looks and feels a little different from XP as well. After a couple days of using it, you don't look at it anymore and you just care about how it performs. Besides Vista and ME, all Windows versions are natural upgrades and always perform a little better than the previous versions. The major downside I would say, is that Microsoft tried to force people to use touch screens and using the metro mode. I've been using Win8 for over a year now and I can honestly say, I don't use the metro mode and it doesn't bother me. I've got the choice, it's there. I can attach a touch screen... nice, but I don't want it and I don't miss it. Most naysayers are always focussing on those two things but they're easily avoidable.
With regards to the start screen, just as with Win7, I just tap my windows-key and type what I need. The nice thing about Windows 8.1, is that if a program is not installed, it will still give you links to sites where you can get the software (so it's not restricted to a local search for software, files, etc).
Oh... I almost forgot this one too. When you install Windows 8/8.1, it will ask you to log in with a Live account so you can sync your files online. To skip this, you can simply enter false information and when it returns an error on login, you can select to create a local account. I have really cursed Microsoft for doing this, but hey, once you're up and running with a local account, it's all pretty similar to working with Win7. Just a little bit faster since the newer OS is a little friendlier with resources.
But again, leave the choice for your next computer. Windows 7 is a decent OS, it's not worth the money for an upgrade.