Most software are not mentioning if they are compatible with Windows 8 or not right now on their specifications. So I will like to know if its safe to upgrade to Windows 8 completely assuming all Windows 7 applications will be supported on it.
You should try to download windows upgrade assistant - it will tell you if the programs you have installed are supported.
In general all windows 7 applications should work, but there isn't a comprehensive list.
Windows 7 and 8 are pretty much identical as far as I can tell and Windows 8 (in my experience) runs anything that works in Windows 7
I have even had a number of older apps that were a pain to get working initially in Windows 7 work in Windows 8, using the same compatibility settings between the two Operating Systems.
Note, this isn't the case with Windows RT. Also, be aware of complications that may arise if switching from 32 bit to 64 bit, some of our apps refuse to work on 64 bit machines (they are very specialized software, but it is something to be aware of.)
Poke around on this page, people vote on what works and what does not.
Some 3rd party's SDKs and printer drivers do not work, as we have found out to our cost.
Certain Brother Printers (the TD range) have Windows 8 drivers, but their SDKs do not yet work in Windows 8. This means that if you rely on the SDK for automatic printing you are stuck. the workaround we had to do was to run a VM hosting an older OS (XP in our case as we had a spare license for it) and map the USB port through to it.
It won't be ideal for some people, but it's a workround until they update their SDK.