I think you are referring to http://blog.kejser.org/2011/10/05/boosting-insert-speed-by-generating-scalable-keys/ which is itself an update to http://sqlcat.com/sqlcat/b/technicalnotes/archive/2009/09/22/resolving-pagelatch-contention-on-highly-concurrent-insert-workloads-part-1.aspx.

It's quite wrong to suggest that IDENTITY or NEWSEQUENTIALID 'are slower' than GUIDs without mentioning that this is only important in the most extreme of circumstances. For the 99.9999% of us who aren't bound by latch contention on the last page of an index on extreme Fusion-IO hardware, other more normal factors such as page splits and non-INSERT performance are likely to be much more of interest than esoteric page latch or sub-latch issues. That's not to take anything away from Thomas' great work here - but it is important to retain a sensible perspective when considering his results.