IBM's JDK 6 web services implementation is based on the JAX-WS RI/Metro web services implementation.
Earlier Kohsuke mentioned that even IBM chose the JAXB RI for databinding . But that was two years back and is not about the whole JAX-WS RI/Metro.
Looked at IBM's JDK in recent WebSphere Application Server v7.0 (Open Beta)  release. This version is supposed to be based on Java EE 5 and Java SE 6. Since I am a JAX-WS RI/Metro guy, wanted to see what implementation it is using. So just tried wsimport:
$ ./wsimport -version
JAX-WS RI IBM 2.1.1 in JDK 6
There you go, it uses JAX-WS RI. It has pretty much the same web services bits(JAXB, SAAJ etc) as Sun's Java SE 6. But it uses different StAX impl, not SJSXP. Note that Metro bits are tested with woodstox , sjsxp  parsers. Now it works with IBM's StAX impl.
As far as JAX-WS implementation goes, it has all the RI extensions like FastInfoset, AsyncProvider etc.
JAX-WS RI/Metro is part of many application servers, JDKs, frameworks etc. We must have done a good job :-)