"G. Sylvester" wrote in news:ksCxh.52308
:

I had another close encounter with a (party / decoration-type) balloon.
I was flying back to SQL with 3 passengers in an Archer at 2500
AGL/MSL when out of the corner of my eye this black thing flew (no pun
intended) by. I asked a passenger what it was and they said it was a
balloon. I think this is the 3rd or 4th time out of ~250 hours that
I've been very close (less than 100 feet) to a balloon. One of the
times it was at 10,500 feet over Los Angeles. Any else see balloons all
the time? I'm guessing they can't do too much damage unless they go
into the engine air inlets or hit the ADF antenna. Now that would be
bad luck.

At least birds stay out of the way....unfortunately not all of the time.

In 500 or so hours, I've seen at least 4 or 5 Mylar Baloons at altitude
(although I don't think at 10,000'). So you are about right.