No 2008 issues here with Word, Excel, and PowerPoint on Sierra on my 2012 MacBook Pro. However the iMac I use most is still at 10.11 and I run mail through Entourage 2008 on that computer.
I've used Entourage as a mail client since it was new about 15 years ago. As I've upgraded my computers the first Entourage issue appeared with macOS 10.9 "Mavericks" and is one that is documented. Entourage refused to launch from its Dock icon. I found a workabout on the MS Office:Mac forums.
Remove the Entourage icon from the Dock and then make an alias of the Entourage app and place it on the desktop. I put mine right above the Dock for easy access. Now I have to double-click to launch Entourage but it is not a serious handicap.
I have noticed Entourage launch times are a little slower considering the iMac is still a fast computer. However, it is the thought of losing Entourage that has held me back from taking the desktop to Sierra. Last time I checked RoaringApps their database was a little bereft of useful and specific information on Entourage 2008 and Sierra. I need to check for new postings obviously.