I have a pretty simple Craft site running a Digital Ocean Ubuntu droplet and for some reason it can sometimes take several minutes to save an entry.
I think this might be something to do with sessions as, when it happens, the site stops responding completely for that browser unless I quit and re-open it. Whilst it is happening, accessing the website via another browser works fine. There's nothing in the phperrors.log or the craft.log that even relate to the time the problem happens but there's something in the Application Logs that seem relevant.
Here's a sample of the 'Profiling Summary Report' where you can see it took 300s to respond but none of the queries takes anything other than milliseconds: http://pastebin.com/pbf7bj2e
The interesting bit is is the Application Log where you can see the timestamps jump from 13:00 to 13:05 on line 58:
What is happening there that took 5 minutes?