[notify]jaydub[/notify]
I see no real risk with doing a payment plan or lease to own and I haven't heard of a single horror story yet, but I understand how you want the specifics. You're certainly not at risk of losing the domain since it's never transferred until full payment is made.
I "assume" you can take the domain back and keep the money if they miss a single deadline but Dan doesn't want to shut down transactions at every possible occasion, especially when they've spoken to the buyer and they've confirmed they'll just need an extra day or two. Dan will try to facilitate things to keep the cash coming in, and probably encourage you to be patient and explain your options, but ultimately it should be up to you if you want to end things right away because of breach of contract. It's possible buyers are given a small grace period though I suppose, like up to 5 days, and maybe even a 1, 2 or 3 strike system for being late.
I do however think that payment plans are best when you're making 1-2K per month for no longer than 12 months, rather than $100 per month for 60 months (for example). People only paying $100 per month might just be testing out your domain, not be very serious, and are much more likely to bail from what I gather.
And as interesting as payment plans are, I'm always still aiming to sell in a single transaction... but on higher priced domains I often set up the instalment option so they can pay it off in 2-6 monthly payments, amounting to somewhere between 1-2K per month. If you keep payments under 2K, buyers can pay using their credit card without any additional fees (and you can accept the funds via paypal without being charged an extra 4% commission).