Private and Commercial
First the good news! Orals have been going pretty well. Where I have been seeing issues is with flight planing and performance. If you are going to use Foreflight or Garmin, you may want to know how things a calculated. I had one applicant show me 3 different flight plans. One from foreflight, one from Fltplan.com and one he did on his own. There was 20 minutes difference in the time enroute and 9 gallons difference in fuel burns. I ask why such a big difference and the applicant had no idea.
Now on to the flying. The number one issue with the private and commercial checkrides has been landings. We've been too high, too low, too fast and too slow. I've been bounced, porpoised and slammed on to the runway. Often times touching down sideways with no crosswind correction. Rather than re-write the Airplane Flying handbook, I'll just refer you to it. Review Chapter 8 and you may want to make note of the "Faulty Approaches and Landings" section.
Having a good year so far. The only hiccup was an applicant that failed to lower the collective at the start of an autorotation. Most helicopter POHs have you enter a practice autorotation by lowering the collective and then closing the throttle. NOT the other way around. When you close the throttle first, rotor RPM drops quickly. (Note, refer to your POH, there are some helicopters and some situations that require the pilot to slightly reduce throttle as you lower the collective.)
Instrument ratings and CFI-Instrument
Biggest problem has been altitude control. I blame most of this on distractions. Keeping a timely scan and not fixating on something too long should fix this. For example, when setting up an instrument approach and programing the GPS, some pilots spend too much time setting up the GPS and not scanning the flight instruments as often as required. This leads to sloppy flying and altitude, heading and/or course excursions.