I used to shoot MPH all the time. There is -no- rush, it takes 10-20 minutes to peak, same as oral, lasts as long as insufflation but it's smoother with fewer twitchy-tweaking effects.
This old thread is one of the first to appear when searching for methylphenidate solubility so I'd like to clear up some confusion for posterity.
Methylphenidate is not a dopamine releasing agent but a reuptake inhibitor.
IV usage will maximize your blood serum levels sooner than other ROAs but it cannot "reuptake inhibit" faster. The only dopamine it interacts with is what already exists in your bloodstream.
Thus there will almost never be a "rush" experienced.