I got to level 20 before I stopped. I could do more, but I don't think the time/reward ratio is worth it. No prize! :P
What I was thinking as I played it is that it'd be better if the amount of jam you needed to collect also increased with level progression. As it stands atm there's just more falling everywhere and it seems just as easy to collect jam than any other level, and actually takes less time. And a knife falling on you should maybe take 2 jam away, it didn't always seem to matter if I got hit.
Anyway, yeah, nice simple game. Would be more addictive if there was more challange with progression.