The Samsung charger's output is rated at 5 volts and 0.7 amps. I've got a charger that's 4.8 volts and 1 amp, and a few others around the same output. A higher amperage charger will charge the battery faster. Proof of this can be seen when using a computer's USB port to charge, which are typically rated at 0.5 amps and take forever to charge. I've used all different chargers with no ill effects that I can tell, but of course if there are any ill effects (ie shortened battery life), they won't be apparent until several hundred cycles later. Basically, keep the voltage the same (or very close) and the current (amperage) the same or higher and you should be fine. Voltage variances are more damaging than current variances, but I'm not going to worry about a 0.2 volt drop with one power supply that I use ~20% of the time.
Also, WP Central posted an article yesterday I think on ways to increase battery life. Following as many of those tips will also decrease charging time. I think a Seidio extended battery is in my future as the battery life of the device as I use it (location services on, WiFi/Bluetooth typically off, feedback on, get location results faster on, brightness medium,screen timeout five minutes, theme usually dark but lately light, Facebook synced, four email accounts synced), doesn't get me through a day without charging. But I'm so used to charging throughout the day anyways that it's not a huge issue. And two months into owning the device and I can't keep my hands off of it, still. Lighting that Super AMOLED screen eats battery like crazy.