Diablo – Does Nephalem Valor Persist Across Game Exit

The entire Nephalem Valor concept has been removed since Patch 2.0.1 (live on Feb. 25, 2014). Along with this change, two new concepts have been added to the game (Official Patch Notes):

Pools of Reflection have been added to the game

• Pools of Reflection provide a 25% bonus to experience
• This bonus persists until you reach a set amount of bonus experience (equal to approximately 10% of the current amount of Paragon experience needed to reach the next Paragon level) or your character dies
• Gathering additional Pools of Reflection bonuses increases the amount of total experience bonus a character can receive until character death, stacking up to 10 times
• This experience bonus persists on logout

Nephalem Glory has been added to the game

• Occasionally during battle, monsters will drop Power Globes when damaged or killed
• Power Globes grant the Nephalem Glory buff, which causes players to deal additional damage in the form of golden lightning bolts and increases their movement speed for a short time
• This buff can stack up to three times

I believe anyone in a multiplayer game can skip dialog or cutscenes, and the skip effects everyone in the game. Sometimes it's just enough to say "hey, I haven't played this yet, do you mind?" - but at other times you might want to just go solo for your first playthrough.

If, however, you're committed to playing with others, and those others are being unreasonable-poopy-head-dialog-skippers, you can review the quest dialog and cinematics at your own pace whenever you wish.

In addition to using the main menu cinematics option (as has been already suggested) to see the in-game cinematics that occur between chapters and at major plot milestons, there is a good database of all the dialog in the game, for each class, on the Diablo 3 DB pages.

For example, this link will show you the quest dialog for the very first quest in the game.

I tend to play Diablo 3 via a "non-Steam game" shortcut, which gives me the Steam overlay. With the overlay's browser, you can be on the DB while you game.