Installed it today
So I just installed Skype for business today. It's really just Lync with a new skin. I don't think you'd even need to upgrade the server unless you had some old version that doesnt support the updated client.
I found the new UI to be rubbish, very little contrast in some areas, like using Office 365 without using the light-grey or dark-grey theme.
The new notification sounds are even worse, so I will be changing those pretty quickly.
You can switch between the lync/Skype themes by changing a registry key and restarting the client.
I much prefer 'Lync' as a name as well. Lotus Sametime had some perks but I prefer Lync