Great reply @Mathew! I agree totally regarding the economic benefit of using Armadillo over competing blogs - and have Armadillo running in several sites. Unfortunately, I have other sites that require features that the pay-per-domain CMS offers, and I have it installed in several sites as well. But, if my client is looking for a blogging solution - or a simple CMS, I'm going with Armadillo every time due to the licensing arrangement. On the other hand, Sitelok also charges per domain - but they generously offer a 50% discount on all domains, after the first. Because of this, I always (happily) install Sitelok anytime a client needs pages to be locked down.
As for Sitelok, I assure @Runamok that it can be used with Armadillo. I'm not sure why you'd need it to, though, since Armadillo a great system built in to limit admin users.
As with Mathew, I use Sitelok on some sites in order to protect pages. With some tweaking, I've also found that it's a fantastic solution for a client (a small city) that runs a fall festival each year. Prospective vendors are able to complete an online application, determine how much they will owe in booth fees (this amount depends upon five different criteria including type of items that will be sold, size of booth needed, number of electrical drops required, etc.) and pay the non-refundable $25.00 application fee. With well over 1,000 applicants, it's critical that my client isn't having to figure out booth fees for every applicant...and with Sitelok, there's no errors. The amount is figured up automatically and then kept track of. If the vendor is invited to participate, they'll be notified six months before the festival, using SItelok's built-in mailer, with instructions on how to pay the remained of their fees. They can even log back into the system and update profile items that don't affect the fees-due (e.g., they can update contact info, booth requests, etc., but can not change the size of their booth, etc).
My last comment is that the authors of Armadillo (Jonathan) and SItelok (Adrian) are both fantastic when it comes to customer support. Both seem genuinely motivated to see their customers succeed. If you are having issues, and take the time to explain to them exactly what your end-goal is...and detail the issues you're encountering, my guess is that you'll get a detailed message back.