When I was a third year medical student in Syracuse, I became friends with my cardiology professor who was also a pilot. As he did not have his instrument rating, he invited me to fly with him to Cleveland in his Cherokee 6. We left Syracuse and headed for Burke Lakefront in VFR. As we passed the Buffalo area, it started getting cloudy with snow showers (not forecast). Luckily I had brought along my instrument charts and filed an IFR flight plan with Cleveland center. Now the fun part. The weather degraded such that we had to make an ILS approach with me flying in the co-pilot's seat. There were no duplicate gages in front of me, so I had to lean over the center console to see the HSI, DG and Vor/Loc indicators. I took over flying at the outer marker and we did ok, but it was not a very safe arrangement. I vowed never to do that again, and haven't.
Moral: If you go flying with some else, make sure you know their capabilities and what might be expected of you.