Generally - If you can live in the limits of 75 users and a single domain with the SBS server as the domain master - its a great deal.
Particularly if you're wanting to get into Exchange. Since you mention Premium, you'll be getting SQL server and ISA server.
Don't scrimp on the server hardware - especially RAM. As SBS server is essentially just standard Win2k3 server, the RAM limit is 4GB so no need to get more.
Also check into SBS aware versions of Anti-Virus and Backup.
Both Trend (CSM for Small Business) and Sophos make great SBS AV products.
Veritas makes an SBS specific BackUp Exec that includes the agents for Exchange and SQL Server.