I have friends that do not want to switch to Windows 8 because they have heard bad things about it. Windows 8 they have an argument for because the user experience is a big difference and seems to be aimed at tablets. Windows 8.1 though has plenty of fixes from Microsoft that address the issues presented in Win8, plus it is a free upgrade if you already have Win8 so I am all for upgrading to Win8.1 if you are using Win7.
I am primarily a Linux user though so Win8.1 to me has been used for Microsoft Office when LibreOffice won’t do (e.g. complex pivot tables in Excel of resumes in Word) and for using specific applications that are not supported in Linux (e.g. syncing of heart rate monitors). Here are some other thoughts.
The search functionality is great over Win7. Win8 had search results return in groups while Win8.1 searches your entire computer and returns results in one group. The search has seemed powerful so far.
The lack of a start button and menu turned off many Win8 users so Win8.1 added back in the start button. There are freeware programs that can mimic the start menu that has been around in Windows forever but I believe the search functionality makes a start menu useless. Even in Win7 I searched more often than I clicked through the start menu.
The start dashboard is probably good if you have a tablet but annoying if you are forced to drag and drop your apps around. The widgets they have they update are cool but the desktop widgets from Win7 is what I believe most users liked.
The apps that are in the Windows Store are lacking and I would rather have a good desktop OS than these flashy apps that I can just use a webpage for. I have seen other users excel at using these apps so if you found a good one, let me know in the comments. Since I am mostly in Linux I have not explored the apps at all.
Win8.1 and even Win8 felt like Win7 with a huge speed boost. Redundant processes were killed and critical processes like copying files and managing your start-up applications were enhanced. No need for third-party apps in these locations anymore.
The configuration for the mouse was hidden because in order to increase the speed of the mouse, the setting is not accessible through the control panel. One needs to open the mouse settings in the Control Panel, described in Source #1 below.
Sources:
Man and Keyboard 