Once a post gets to a certain size, mercy requires that it be ended before the readers head explodes. The DOMA post hit that limit well before any discussion of Prop 8 could take place.
California Proposition 8 and same sex marriage in California generally have a fairly convoluted history as such things go - so to a large extent I'll just skip that and leave the reader to explore the mind-bending twists of that voyage on their own. The holding in Hollingsworth v. Perry is sufficiently straightforward, technical and narrow that both the history and possibly even the subject matter of the case are largely irrelevant to the ruling - though very important to Californians wishing to legally marry their same-sex spouse.
Rather than addressing the merits of the Proposition 8 case, the Court addressed the issue of standing - whether or not a particular person or group of persons had the right, having suffered some identifiable wrong, to bring a case before the federal courts. Simply put, the Court ruled that the intervening plaintiffs in this case did not have standing to bring the case and, as a result, the Court was not required to render a decision upon the merits of the case and so would not.
A key quote in the Prop 8 decision regarding standing "In other words, for a federal court to have
authority under the Constitution to settle a dispute, the
party before it must seek
a remedy for a personal and
tangible harm" lays the ground for the final order finding the intervening plaintiffs lack standing as they cannot formulate a particular personal and tangible harm they suffer.
In terms of any enduring legal principle being set, the Prop 8 case breaks no new ground and only re-plows long-tilled judicial earth best summarized as "no standing, no case."
In terms of a practical effect on the rights of LGBT residents of the State of California, the effect is immense as a malicious initiative designed for no other purpose than to select them out from the general populace and ensure that they are reduced to a lesser "separate but equal" status when it comes to marriage rights is now decisively overturned, even if on a relatively technical point rather than the merits of the case as they might have been argued before the Court.
Summarized? A tremendous, but local, victory that does not set any sort of national precedent in terms of a Supreme Court ruling.