So, what is it, how do you get it and should you care about it?
(tl;dr version: New version of Windows which you can upgrade to for free. Ask me for further advice!)
Windows 10 - What is it?
With the advent of Windows 10 Microsoft is returning to the Desktop as the computing environment of choice, bringing back a Start menu (albeit a modern interpretation of one), and enabling the new Universal apps to run in windows alongside the more traditional Windows applications (such as Word and Excel).
But it's not all about re-introducing familiar concepts and elements. Windows 10 builds on the underlying changes pioneered in Windows 8 and makes them more available and discoverable, whilst also introducing new features to help you get things done more efficiently. These include Cortana, a voice-activated digital assistant which not only helps to search your computer and the web for information but can also integrate with your email, calendar and contacts and help you organise your day. Not only that but, because Cortana integrates with your Microsoft account (which you will use to log in to the PC, just as you do with Windows 8), the information she collates will also be available on your smart phone through a downloadable Cortana app on iPhone and Android phones or directly on a Windows phone.
Windows 10 will still come with Internet Explorer 11, the browser that everyone seems to use primarily to download Google Chrome. However, the default browser will be Microsoft Edge, a brand new browser based on Internet Explorer but without all the compatibility baggage from previous versions that slowed it down and caused so many problems. Edge is designed to be fast, provide you with ways to save articles for offline reading, and even enable you to annotate web pages directly within the browser (and share those annotations with others, even if they're not using Edge).
Windows 10 - How do I get it?
The Windows 10 upgrade from Windows 7 SP1 and Windows 8.1 Update will be quite straightforward: run the installation, follow the instructions, wait a while (probably an hour or so) and you're done. The installation routine will install Windows 10, migrate all your files, applications and settings and update itself automatically. Upgrading from other versions of Windows will not be quite so straightforward, so if it's possible to do so I would recommend upgrading to Windows 7 SP1 or Windows 8.1 Update first. If you're in any doubt you can run the Upgrade Advisor in the app to check your PC's readiness to run Windows 10.
Incidentally, if you don't see the Windows flag icon in the system tray, don't panic. It's possible that you have pre-requisite updates that you need to install first. To check, open Windows Update, check for new updates and then install any that make themselves available. Following a reboot the flag icon should appear. The other alternative is if you are working on a business machine that's connected to a Windows domain (i.e. you log in using a business account connected to a work server). If that's the case then the upgrade application is suppressed, as any operating system upgrade in businesses will need to be planned centrally, rather than occur in a piecemeal fashion.
Windows 10 - Should I care?
Windows 10 is an evolutionary version in many ways but one that will make sense to both Windows 7 and Windows 8 users and provide enough new features, coupled with old favourites, to make it easy to use and understand. That's not to say I would recommend installing it as soon as it comes out on 29th July. I will be, but then see above for the comment regarding Sunday evenings… Windows 10 will be the first version of Windows to be released with the explicit intention of it being updated with new features as they become available, rather than waiting to release it until those features are ready. Therefore it is entirely possible that when Windows 10 is released there will be problems or glitches that haven't surfaced through the preview programme and that need to be fixed. I expect things to get fixed pretty quickly if they need to so if you want to try it out then do, but you have been warned: the bleeding edge is not for the faint of heart!
Having said that, from everything I have seen, tried, tested, broken and fixed whilst running the preview builds, Windows 10 looks to be an excellent version of Windows and keeps to the tradition of every other version being deemed "good":
Is it good enough to upgrade from Windows 7? Almost certainly. Is it good enough to upgrade from Windows 8? Definitely. Do you need to? That is entirely up to you!
Windows 10 - Next steps