I just tried it out for the first time today, and it turned out okay. The marinade I used called for 1/2 teaspoon salt for 1 1/2 pound of top sirloin. Being the newb, I thought, this is not enough, and I put in about three times that amount.
The meat tasted extremely salty. Wow, I didn't know 1/2 a teaspoon of salt can make 1 1/2 pound of meat taste so salty. If I just cracked that much salt over the meat while it was grilling, I don't think it would've tasted that salty.
Another problem I came across, was that the meat did not fully cook through. The center of the meat was pretty red, and there was some blood, while the outside was "well done." I cooked each side (4 sides) for 4-5 minutes on medium heat.
That said, I didn't exactly cut the meat to 1 inch size. They were mostly 1 1/2 inches and 2 inches. I forgot that an inch is actually quite small, but it was too late by the time I figured it out. It would've probably still cooked through had it been a real grill and I closed the lid, but I guess this is the limitation of the grill pan, and I just have to make adjustments in the future (1 inch cubes).