It depends where you get the software from:
Main - Canonical-supported free and open-source software.
Universe - Community-maintained free and open-source software.
Multiverse - Software restricted by copyright, legal issues or may contain patents.
Restricted - Proprietary drivers for devices.
It's the last two that could pose a legal grey area, such as packages for DVD playback, licensed codecs, or hardware drivers that would need a separate agreement. This could include anything that would remain questionable for home use. Some software may be fine in some regions but not in others.
For instance, in the UK, it is illegal to stream TV if the business does not have a "TV license". So possessing an antenna with software that streams live TV would be illegal according to UK law, but it's not a violation against the license of the software itself.
Another example may be using VLC to play a radio station to everybody in the office. VLC is licensed under the GPL, but the UK law requires the business to have a PRS license. So it's not the software, but the individual who puts the business at risk for not complying with the law.
May be of interest, but Windows' licenses in my business use the "N" edition of Windows, which omit multimedia functions. That's more to do with consumer choice in the EU then licensing, I believe.
Any business can use Ubuntu (or flavours) without charge or legal threats. That is:
- Unless they start modifying GPL software, distributing it publicly but refusing to reveal the source code, that's a GPL violation.
- Unless it's being used in a country where the government has banned a specific product or service (unlikely, but some countries do)
Depends on the license and serve the violation is. A business could end up in court as open source licenses like GPL are an enforceable contract.
Some more info: