I have been doing a longer preinfusion for awhile now, but recently I began experimenting with pushing the limits of both preinfusion and length of pull. The results are that I have found far less issues with the puck (only one bad one so far) and a much more consistent result in the cup.
Until recently I was preinfusing until droplets formed on the basket, about 10 - 30 seconds--in agreement with Rustic39's thoughts about letting the puck determine when to initiate the pull. A few weeks ago I wanted to see what it would taste like to do a 1 minute preinfusion and 1 minute pull so I performed a really fine grind, about +40 degree rotation on the locking collar of the Pharos over my old standard grind. This is about 90 degrees from the burrs coming in contact with each other.


The shots were oily and thick. I think this pull ranged from 7 - 5 bar until I stopped the shot.

With my lighter roasts I found the flavor seemed to be a little more intense and I had detected some flavors that I have never noticed before with the same beans. The profile seemed to have changed for the better. When I did this with a dark roast I found that the chocolate and molasses (supposed to be fig, but tastes like molasses to me) flavor seemed to be more full, but less intense (if that makes sense) and bitterness was much subdued. I would describe it as being much more creamy and developed. I normally don't like darker roasts in shots, but I find that doing this method makes them much more to my liking.
The bottom line that I take from from this thread is that we should enjoy the ability we have in our lever machines to manipulate all aspects of the extraction process and to occasionally take the time to experiment and challenge existing tenants. The established methods are established for good reason, but that doesn't mean there aren't better approaches out there yet to be discovered.