Now just so you know, I'm knocking on my wood-composite desk for continued luck. Lately, we've had huge potty training successes at our house. About 2 weeks ago, I started bribing Juliet with a Dum Dum sucker if she pooped in the toilet.

She whipped right into shape and hasn't had an accident since then. She's even starting to forget about the sucker reward.
Jack, whom I've struggled with for 10 months, has finally started to show some improvement! He's always told me that when he's 4, he'll start pooping in the toilet. Sure enough, he hasn't pooped in his underwear since Thursday. He just goes and does it. There are a couple of factors playing into our success.
#1-Juliet has shown great success and he didn't want to be shown up by his 2-year old sister.
#2-He has a Woody toy (from Toy Story) that would sit on the fridge until he pooped in the toilet.
#3-Recently, if he pooped in his underwear, he'd lose his underwear privileges and have to go commando until he pooped in the toilet to earn his underwear back (Thank you Emily).
Also, about a month ago, I quit putting Jack in pull-ups at night because I didn't feel like it was helping. At the same time, Juliet refused to wear a diaper or a pull-up to bed, so we were washing sheets every couple of days for a few weeks. However, they've both made it through the night dry for 2 weeks.

It's been a long, ugly, stinky road but I'm feeling relieved that the end might be near. It's only taken 4 years to get Jack completely potty trained and I think it has a lot to do with Juliet. Juliet has been my easiest to potty train because she wants to do everything herself. She's so tenacious!
I'm not saying there won't be relapses, but I haven't washed out poopy underwear for 5 days and that feels wonderful!! Let's hear some noise!!!!!! YEAH!!