First off, Condon, amazing guide. Nothing quite like learning an awesome champ whilst laughing so hard I leave my own yellow trail, and spewing beer all over my keyboard. Very informative and accurate, thanks for your work :)
Now, what are most of you guys taking as your secondary mastery? I'm about to fill utility, and I'm leaning toward the juicy-looking Evasion/Nimbleness combo that adds even more fuel to the Rokkit while I'm zooming around in circles ruining full-team gank attempts, simultaneously improving survivability slightly through Hardiness, 1/3 Resistance, and the tiny bit of dodge.
However, if I find that Exhaust complements goo well, and doesn't end up being completely obsolete because of it, going nine deep in offense for Cripple, Archmage's, Sorcery and AK could be a pretty incredible damage boost, which is never bad.
Normally I would just test it out for myself, but as I haven't yet gotten high enough to do so, collective thoughts and ideas from the community may just save me a whole ****load of time.
Edit: Another reason I ask is because Exhaust is not in the list of summoner spells in the guide, so I'm unsure of its usefulness, and a bit hesitant to sacrifice Heal in the early game to test it out - I'm still perfecting the hit-and-run method, Heal pulls my ass out of the fire more than I'd like to admit.