Here's their category on gay marriage and homosexuality: http://pewforum.org/Topics/Issues/Gay-Marriage-and-Homosexuality/
On declining religiosity, there's affiliation (as Doug notes), and attendance is probably worth noting, as well, but there's also beliefs, and then the people who consider themselves "spiritual" rather than religious.
But I think the place to start, at least among Pew's data, is their survey from a year ago about "the milliennials<http://pewforum.org/Age/Religion-Among-the-Millennials.aspx>." Note that they rely on some Gallup data for cohorts.
On the affiliation point, it's pretty overwhelming --
Compared with their elders today, young people are much less likely to affiliate with any religious tradition or to identify themselves as part of a Christian denomination. Fully one-in-four adults under age 30 (25%) are unaffiliated, describing their religion as "atheist," "agnostic" or "nothing in particular." This compares with less than one-fifth of people in their 30s (19%), 15% of those in their 40s, 14% of those in their 50s and 10% or less among those 60 and older. About two-thirds of young people (68%) say they are members of a Christian denomination and 43% describe themselves as Protestants, compared with 81% of adults ages 30 and older who associate with Christian faiths and 53% who are Protestants.
-- but I think affiliation is not the whole story. If "religious" means "subscribe to a religion and go to church," then we are definitely getting less religious. If it means, prepared to accept evolution and homosexuality, we appear to be getting less religious. If it means, no longer believe in something like "god," souls, heaven, and angels or other supernatural beings, then I think on that point, maybe we are not getting less religious.
For example, 74% of the general population believe in life after death, but 75% of those between 18 and 29.
And there's a chart here (I would attach but I'm not sure that's in-bounds) on "importance of religion by generation," and in all but one generation (of five) it has gone UP in the last twenty years. But still, each generation views it as less important than the previous one, by the look of it.
Introduction and Overview
By some key measures, Americans ages 18 to 29 are considerably less religious than older Americans. Fewer young adults belong to any particular faith than older people do today. They also are less likely to be affiliated than their parents' and grandparents' generations were when they were young. Fully one-in-four members of the Millennial generation - so called because they were born after 1980 and began to come of age around the year 2000 - are unaffiliated with any particular faith. Indeed, Millennials are significantly more unaffiliated than members of Generation X were at a comparable point in their life cycle (20% in the late 1990s) and twice as unaffiliated as Baby Boomers were as young adults (13% in the late 1970s). Young adults also attend religious services less often than older Americans today. And compared with their elders today, fewer young people say that religion is very important in their lives.
[ . . . ]
Pew Research Center surveys show, for instance, that young adults' beliefs about life after death and the existence of heaven, hell and miracles closely resemble the beliefs of older people today.
[ . . . ]
In their social and political views, young adults are clearly more accepting than older Americans of homosexuality, more inclined to see evolution as the best explanation of human life and less prone to see Hollywood as threatening their moral values.