Microsoft has a great blog over on TechNet about running enterprise applications on SQL Server. I just watched a best practices webcast "Deploying Kronos Workforce Management Solutions Using SQL Server 2008". Allan Hirt (has been around the SQL Server space forever), Dan Pronley (dir presales technology at Kronos) and Anu Chawla describe how Kronos is moving more and more towards deep integration with MS products (SSRS & SSAS anyone? Office, SharePoint).
Some key points they are espousing include the suggestion to consider a move to SQL 2008 a.s.a.p. Not for performance reasons, as the benchmark in the webinar shows minimal improvement there, but for the future. Did you know that SQL Server 2005 support is starting to fade?Kronos says 350k active emps are supported in 6.1. They are clearly being conservative. See #5 below.
There is 64bit support on db tier and at v6.2 on webapp layer.
Kronos supports both VMWare and Hyper-V and if you're on 2008 HyperV can now failover.
HRPR can't handle 64bit so if that's in your mix go 32 bit for everything.
www.kronos.com/ms/benchmark give highlights, with a white paper, on how TCO using SQL server can be MUCH better than Oracle. The test is with 384k emps across 500 locations!