In SAP servers Linux is growing like any thing and I found Linux is better option for SAP servers from Security and Administration point of view. Right now, two Linux distributors ( RedHat & SuSE) are working hard with SAP to ensure all SAP products get optimized on their distribution.
SAP has certified both the distributions on x86, x86_64, IPF, IBM System p and IBM System z platforms. For SAP on Linux currently three databases Oracle, MaxDB and DB2 are certified by SAP.
(P.S. : Before planning any SAP implementation with Linux , refer compatibility matrix and also refer SAP Note 171356 – SAP software on Linux: Essential information)