If it shakes all the time in neutral but not while accelerating it may
be a timing issue.  I'd check the timing system, including vacuum lines
as the mechanic may have bumped these enough to cause a leak, as well
as the idle RPM, make sure it matches up with the manufacturer
specifications.
My 1983 volvo sometimes idles slightly slower than spec once it is warm
and the result is a terrible shake, a problem which i'm still working
on.

I've also heard of this fault occuring when there is a blockage/leak in
the exhaust system which changes pressures at the engine. It cant hurt
to check for any damaged gaskets. My guess is that if a leak in the
exhaust system can cause this, the same can be said about the intake
system, so it may be worth checking out your air filter and intake.
I'll be watching this post for any progress in the hope that it may
help me out as well.

Josh

Thanks for the comments.  I am going to take it back to a different shop
today and have them check it over.  I will post whatever the new shop finds.
Regards,
Matt