Snapz Pro is from Ambrosia. They develop both utilities and games. One of their games, the one before Escape Velocity Nova was a very popular game amongst pirates and they came up with a scheme where, you have to launch a separate program and it activates the program. What is interesting is that you have to do that every year and you are assigned a new serial number and your program is activated. Remember they are selling games and the registered users are very aware of the high piracy rate in that category so they are probably a lot more accepting of the bother. It really works quite seamlessly and for a user like me who owns several of their utilities and games, it has never burped on me.
I have no idea how Tinderbox does it. I have been using their program for about six years now and they always seem to have a very good handle on their product activation process. It like your program has a very defined niche and seems to be pulling it off by some voodoo I don’t understand.
My point is that for programs which are used to generate a livelihood, users are usually quite willing to pay up and gain good karma. The ones who are not, you might try to shame into paying up, but the trade-off is whether you are pissing off legitimate users in that process.
The activation process for me was a bother. The program tried connecting to the esellerate server. Said it couldn’t activate and gave me no other option other than to quit the program. I deleted the new version. Re-installed the previous version to get back to work. To solve the problem, I went to the forum which led me to the wiki, got an inkling of the problem, went to the esellerate site, downloaded a new program, installed it, deleted the old version of Scrivener, re-installed the new version of Scrivener, launched the new version. It did its activation thing and I was back to work.
That is too much work. I am a persistent kind of bloke, I depend on Scrivener for too much of my work and I wanted to be compatible with Snow Leopard. So, I made the effort. But I shouldn’t have to.
I am sure that in your poll you are going to get an overwhelming majority of your users saying: It is not a bother at all. That is not the right question. It is not a surprise that one would accept activation. I bought the program, you want to check that out, that is cool with me. I have nothing to hide. You check it out and I get to work. The problem is only significant if you check it out and come back with the assertion that I am not legit when I really am. That is when the problem starts. In my case, the activation failed and I was locked out of the program. It wasn’t benign. It made it impossible to use the new version. I had to go back to the old version. That is the false negative which is going to cause you aggravation. 
You are tackling an important issue and it will have an effect on your revenue. I am sure that you will work it out and my experience was an outlier in the process. If the esellerate engine works as advertised you shouldn’t have a problem, but it is not fail-proof, and you need to be aware of that.
Much more than my 2 cents, I am afraid.