I hate how registration gets disabled the day I go to sign up. I have it sitting on a tab where I click on "Register" about four times a day so that if they open up registration again for just an hour or so I won't miss it.
More money for winning battles? And more XP for KO-ing Pokemon? I'll play it a bit first and get a feel for it. If I totally dig it... than the $5 sounds worth it.