iOS 8 is due for release on the 17th Sept, although on the surface it may not look like the big update that iOS 7 was, there are several major enhancements. Some of these will not become available or apparent until OS X Yosemite is released and even then some will be pushed out as updates to Yosemite in October.
One of the important things to look out for when upgrading is the option to update to iCloud Drive. You will see a screen similar to that below.
If you are a user of iCloud Documents, in things like Pages, Numbers etc and you need to access these documents on your Mac computer then you should hold off upgrading to iCloud Drive until Yosemite is released. If you don't read the above properly and just click "Upgrade to iCloud Drive" you may loose access to your documents until you upgrade your Mac to Yosemite.