We seem to be having problems with our iMac once it wakes up from sleep mode.
The symptoms appear to be that of a partially working DNS.
As an example this morning, emails are coming in, I can connect to Facebook and Google, but most of my other bookmarks are just timing out.
This even applies to the bookmark for the sky hub (SR102), which is saved with a URL of its IP address.
Rebooting the router does not resolve the problem, but rebooting the iMac does.
Not sure what to try next other than doing the normal reboot of the iMac to resolve it.