Yes, except in old version it uses a double brackets:

[[xsl:value-of select="productVariant/summary" /]]

You can also query the product's summary, and not the variant's summary:

[[xsl:value-of select="productVariant/product/summary" /]]

Thanks a lot! Just one more question: only Summary its available? not TERMS, BUYING GUIDE, FAQS, OVERVIEW, SPECs?

Yes, only Summary is available. We didn't expose all the fields in the model to query :(