I did a cursory analysis of the number of current (as of 4-Oct-2006) IETF Internet-Drafts (I-Ds) that reference or employ SAML, and to what extent they do so. The executive summary of my findings is (click here to skip intro):

SUBSTANTIVE SAML employment:     8   I-Ds
Some SAML Incorporation:        10    ''
SAML referenced 'in passing':   10    ''

Seems to me this is a non-trivial number and that SAML is acquiring some decent traction there.

My overall analysis write-up is here, it lists the I-Ds my simple grepping turned up, as well as the bits of text where the term SAML occurs.