I have SharePoint 2010 setup with SQL Server 2012 and SSRS setup in Integration Mode. All of this is on one server. The machine is farily large 16 CPU's and 48 Gigs of Memory. Very simple reports that display one number or one small graph are running in 10 to 15 seconds. The same report will run in less than a second within Visual Studio. Also I've noticed the "Actions" menu is slow has timed out at times. I reviewed the logs and it appears the report is running in less then a second from the time the "Found session for" is found, but takes several seconds for the session to be found.
I've found in the logs a delay between WcfSendRequest WcfReceiveRequest of about 9 seconds.