I personally think simply putting up a donate link like Greek does would be better than using adfly - you're not pissing anyone off because omg ads!!!, and those that willingly want to support you a little bit will do so.
Plus:
To put it another way, if every single active user currently playing Blockland went through the adfly link, you'd earn, what, $30?
Really even less.
Can kinda relate this to music as well, I offer my stuff up both for free or if you want to donate a bit. Both add-on creation and creating music has a similar amount of effort needed, I feel.
(Is adfly considered a referral link now?)