"In retrofitting from 4 tube T12 to 3 tube T8 fixtures, I was assured the new T8 lamps are brighter, but now the store looks darker than before."

The 32 watt T8 lamps can be misleading.  While they produce more light per watt, 32 watts is less than 40. The TOTAL lumens of a 32 watt T-8 is lower than the 40 watt T-12. Since most T-8 lamps are photopic light sources, they will appear LESS bright than lamps which are scotopically enhanced. (5000 Kelvin or higher/ CRI 90 or better).

"Our office switched  T10's for better color and extra light. In many fixtures, the new T10's flicker violently. The company sent us replacement lamps, but they too flicker."

The T10 lamps are designed to be a direct retrofit for T12 lamps on most T12 ballasts. However, the T10 lamp requires a higher operating voltage than a T-12. While most ballasts can compensate, about 15-20% fail to operate the T10 properly.

"What's the skinny on 'long life' fluorescent lamps?"

This depends whether we discuss total life or useful life.

The total life ends when the lamp goes dark altogether.   This occurs when the electron-emitting coating on the cathode is used up.   Adding extra coating permits extra overall hours.

The useful life ends when the gasses and phosphors degrade and the lamp no longer operates within design specifications. 

After two or three  years the color temperature, CRI, and brightness degrade to where the lamp does little more than keep you out of the dark.  This is true with ALL general purpose fluorescent lamps, long life or not.

"What's with fixtures that need to be blinked off and on to start?"

Try touching the glass tube, if the lamp "pops on",  it's probably a grounding issue. Tubes which are worn, dirty, cold, or have poor socket seating often hesitate.

"How 'black' should the ends of a lamp be allowed to get before it's time to change the bulb?"

Again, lamps should be replaced every two to three years regardless of end blackening.  Moderate blackening is a normal part of a lamp's life cycle.  Dense blackness on an end is a sign the lamp should be replaced right away to avoid ballast damage.  If dense blackening is seen on both ends of a tube, the ballast may already be bad.

"Are there applications where The Skylighter might not be the best choice?"

Of course. Every application is unique. In such a situation we'd be happy to steer you in the right direction.