This CNET article is a good overview of 8.1 features (see link below). Best benefit is being able to boot Windows 8.1 directly to the desktop, instead of the accursed Metro/Modern tile interface. Personally, I use Classic Shell for Windows 8, to avoid "the new Vista" touchy-feely tiles horror. Classic Shell is a free third-party interface, makes Windows 8x work close to Windows 7, and you still get all the faster performance from Win8.
The new features you need to know about in Windows 8.1I saw a recent report that said even Microsoft employees have been heard to call Windows 8 "the new Vista" since it is so unpopular. That said, I should point out that Vista with its latest service packs actually runs pretty well, rather like a Windows 7 for older computers. Slower, yes, but Vista is a viable upgrade path for many of those who don't want to run unsupported XP after next month.