direct XXX, contact Socal on 134.65." When you contact
the next controller you should say "Airbus 12345, 2000, direct XXX."
Just like if they give you a heading and are handed off, you should
tell them your newly assigned heading. Don't assume anything. A

I haven't been doing that. That right there could (and probably does)
explain 2 of the 3 cases I can recall of being asked this question.

The last one, the one where I know I was a bit off course, was the
aforementioned occurance where we lost vacuum just moments later..
though actually, honestly, I don't really think that was the culprit
(though I normally do fly by the DG and VOR head and not the GPS ground
track).

This was my first time left seat in this particular airplane as well,
and I was studying an approach plate (no excuse, I know).

And, as I noted, not on this or any other time did I detect annoyance
from the controller.. in fact she (Chicago center) was very polite and
chipper.

I'm sure (well, 99% sure) I have nothing to worry about.

just trim out the plane perfectly including rudder trim so your
TC is perfectly level. It's just like your elevator trim. Get
them perfect and the plane will stay straight.

Rudder trim? You mean the little tab on the back of the rudder? :-) I
fly a '79 C-152, and, no, it does not fly completely hands-off level.
Few of them do!

concerned, no. But of course you'll wonder. Just like when I
flew into LAS in an Archer. I made a nice radio call "Cherokee XXXXX,
6000, information bravo." They came back and asked if I had information
bravo. This happened on 2 controllers no less. I figure they're used
to dealing with 'real' airplanes that I can only dream of flying.

Another thing I've wondered about is how often the pilot is told when
they'll be filing paperwork. It seems the norm is the dreaded "call
this number on landing" but I know that they don't have to do that. If
a controller was really peeved at you, he might take perverse pleasure
in making sure you didn't know what was coming.

Before somebody replies, I know that controllers are not out to violate
pilots and are almost all good guys & gals.

And 2) Just _what_ is the IFR "heading tolerance", anyway??

I should have stated the question as "course-deviation tolerance".