I've just released an update for Jet Boy that removes some bad stuff and adds some good stuff.
W and UP can now be used for jumping/flying. Level 24's background is much easier on the eyes. Level 7 can no longer be by-passed due to flying over the obstacles. The ending of the game feels little more satisfying and complete. Respawn time has been increased, and you no longer fly into spikes after respawning. Fixed several other minor bugs. And, most importantly, Level 12's difficulty has been reduced :P