We completed a SP2 install using the SBS wrapper.
The time it took was about 50 minutes.
The SBS 2008 was running as a VM on Hyper-V with two vCPUs assigned. It was a fresh install with no real users or production based configuration yet.
The hardware was a single Xeon Processor 3400 series with a hardware RAID 5 disk setup.
It looks as though this service pack will take _a long_ time to install depending on the hardware configuration, number of mailboxes, and other factors.
Keep this in mind when scheduling for the update.
Microsoft Small Business Specialists
Co-Author: SBS 2008 Blueprint Book