I am considering applying this Service Pack 3 in a SQL Server 2008 with SP1, however I was not able to find if there are any drawbacks in this process, specially regarding to Replication Services and Reporting Services. Someone had done this update? It was smooth or got many issues?
You shouldn't have any issues, just be sure that when you plan your maintenance for SQL Server you don't get blocked by the "Restart Computer" rule. E.g. if you have installed Windows Updates in the meantime you might not know that Windows needs to be restarted until you enter your maintenance window...
For some background, I got surprised by this during a SQL 2012 Service Pack + Cumulative Update series recently. It turned out that I fired up the computer, started the Service Pack install, but didn't know that Windows Update had started performing updates in the background. By the time I got to the CU, the reboot flag had been set, and I was very frustrated since it seemed to me like the SP install had forced a restart requirement.