In Diamond Age the character Miss Matheson alludes to her past in a reminiscence concerning the 'smart wheels' on her wheel chair. She likens them to those on skateboards and then talks about how she was once a 'thrasher'.
This strongly suggests that Miss Matheson is YT from Snow Crash.
This is obviously speculation on the part of Wikipedia although it makes perfect (and poetic) sense - I love the idea that an ex-thrasher 'wild child' became a prim and proper neo-Victorian school mistress in her later years.
The question is, has this ever been confirmed by Neal Stephenson?