Fixed this on lion 10.7.2 by restoring IOPlatformPluginFamily.kext from vanilla 10.7.2 (I recall deleting ACPI_SMC_PlatformPlugin.kext from the plugins folder after installing lion, not knowing the mouse/kb delay would start from there on) and switched smbios to imac12,2 using multibeast.
The reason why i deleted ACPI_SMC_PlatformPlugin.kext post lion installation: I was getting KP's at boot when using smbios imac11,3. That said, the KP did go away deleting the ACPI.. kext but the mouse/kb delay started to kick in..
TL;DR smbios macpro3,1 and imac12,2 works okay with vanilla IOPlatformPluginFamily.kext and no more mouse/kb delay at login screen, yey!