It now appears as though Microsoft has once again priced (overpriced) their new operating system Windows 8 to well over $100 for an OEM version. Windows 8 Professional OEM will sell for $155 whereas the less expensive Windows 8 Full Version for around $110. Early rumours had Microsoft selling their new O/S at $39.99 with upgrades from Windows 7 on machines purchased June 2012 forward eligible for a $14.95 upgrade. Although these prices are not written in stone until the actual operating system comes out in just over a week, the pre-order sales for what I can get my hands on, which is the OEM versions which are for new computers (or those that are being installed to a clean ed hard drive without a previous operating system). Needless to say I am not impressed, especially when I was so looking forward to Microsoft FINALLY recognizing the fact that selling at sub-$100 would have had the conversion to the new operating system that much faster, very much like what Apple does with any new release of their operating systems. Noting that the latest Mac OSX "Mountain Lion" was their fastest selling operating system with already over 40 percent now using this latest O/S.
With Microsoft doing everything they can to push people away from XP and on to Windows 7 and now to Windows 8, it was sure to be a hit with a low selling price but I am pretty sure this will not be the case, especially if it is going to cost this much for the new operating system. Understanding that most people already have a windows operating system, an upgrade would be all you require, however if you ever replace your hard drive then you are going to have to have a previous version of operating system that was NOT an upgrade in order to first install that before allowing you to reinstall the windows 8 upgrade version.
All of this being said, the main question of whether or not you should be upgrading can quite easily be answered by what your current operating system is. If you have windows XP then yes absolutely. It works with just 512mb of RAM memory and it should give you at least another year, if not two without doing anything else. You will be pleasantly surprised at the speed and you will also be secure once again. XP is nearing the end of life in 2013. If you have Vista then yes, I would still suggest it and if you do have Vista then odds are you also have at least 2GB of RAM memory so you will really notice an improvement in performance. If you have windows 7 then I would NOT be suggesting it as a necessary upgrade although it should also improve performance, if you are not one that likes change too much then stick with Windows 7 (for now).
The key factors here boil down to fund$$ and if it meant spending over $100 for a new operating system when you can go out and buy an entirely new desktop box for about $300, that would already have the new Windows 8 installed, or can be for another $15 then you are better off to go that route. But if you can get a less expensive version at around $40 then you are going to find it worth your while.
If you are unsure of what to do, just ask and I will point you in the right direction.
UPDATE: Oct 14, 2012: Microsoft has released the pricing structure (USD) for Windows 8 on their facebook page as the following:
Currently, there are four different versions listed. Windows 8 Professional Upgrade ($69), Windows 8 Pro Pack with a product key only ($69), Windows 8 OEM ($99) and Windows 8 Professional ($139). The Windows 8 OEM and Windows 8 Professional editions of the OS have both a 32 bit and a 64 bit version available for the same price.
As mentioned above and confirmed from this source, if you purchase a Windows 7 PC between June 2, 2012 and January 31, 2013, you will have the option to upgrade to Windows 8 for $14.99. Registration for the Windows 8 upgrade will be available to all new Windows 7 PC owners until Febrary 28, 2013.
So my opinion on this hasn't changed much, since it appears the rumored $39.99 is actually $69 which shouldn't be too much of a surprise as Microsoft doubles this price. It does make it a little easier to decide however, if you want to upgrade or simply buy a new computer.