I hope you tracked the intruder to his destination.

No I didn't. My supervisor and I had a very short discussion about
doing so and then decided we could prove nothing. Could have
been bad mode C, no way to prove he was not VMC, the Baron
never saw him etc etc.

In what situations would you decide to track the traffic? I'm curious
because one very clear night I didn't feel like bothering with Phila.
Approach and just overflew the Philadelphia Class B VFR at 7500 enroute to
Atlantic City. When I called ACY Approach, they told me that Phila. wanted
to talk to me. I called after landing, and Phila. said they showed me below
7000 for part of the time, thus in their Class B without a clearance. I
assured them I was at 7500 the whole time, and agreed to get the Mode C
checked (it was due the next month anyway). Is ATC more likely to pursue a
possible Class B violation than a rogue IMC?

Barry