1) Not since 1990. The Li-Ion battery chemistry doesn't need any special charging. When the devide arrives, it will be between 40 and 60% charged, this is the ideal charge level. From there either use it or charge it, it makes no difference. The first time it reaches end-of-charge it will store the battery capacity, but this doesn't affect any functions. There is no loss in autonomy.

2) The function is there to correct slight manufacturing differences, slight installation differences, minor stuff that could happen during use. Standard resistive touch screen measures current when the screen is touched, this is an analogue value. As a result, the sum of all tolerances could make the screen slightly one way or the other. Re-assembly of device could slightly move the points, etc.

As a result, a calibration feature is available, so the software would correct for such tiny inconsistencies. If you find yourself clicking a tad above, below, or to the side, run calibration and the software will learn where the touch points are, correcting on the go.

One more advice. A long time ago, electronic battery management was a dream. With the advent of picocontrollers, newer batteries have internal management. Coupled with N900's exquisite battery management hardware and software, it's all automatic. As a result, don't take ANY battery tips from anyone. Any gain from minor enhancements will far outweigh bad or old practices that could cripple the battery.

In newer devices, the best way to care for your battery is do nothing. Charge as needed, discharge as needed. Try to avoid unnecessary cycles (5 5-minute charges are wore than one 25 minute charge), but don't go to extreme lengths. And, before you ask, no, battery never charges 100%, it's not a bug. It charges to less and less as battery ages. Don't go freezing it as per whatever site Google popped up. Also, charging from wall charger is faster. Over USB it can take up to 3 hours. This is normal.

For more information, the forum has a battery life thread where lengthy discussions on battery practices took place, but the short version is leave it alone and try to not discharge to nothing and forget about it for days.