For security reasons, SP2 increased the protection at boot and shut down. I either notice a boot slight slow than before but I don’t think it’s a problem. I had, and big ones with Blue Death Screens because version 4.5 conflict with Norton GoBack 2004. I had to disable (not uninstall) GoBack and then repair avast! installation, boot, enable GoBack again before boot. After boot, GoBack could not be re-enabled with avast! 4.5.
Both program saved me a lot of times… I don’t want to get rid from GoBack (anyway, Vlk always call it, and he’s right, buggy…).