It looks like we're moving towards nationwide "marriage equality" (as folks on the left like to phrase it) in the near future, as the Supreme Court let stand the overturning of same-sex-marriage bans in five states. Six other states in those appellate districts would likely have their bans trashed, so this has 11 states having to change their policies, lifting the total to 30 states that allow (sometimes forced to allow by courts) same-sex marriages.
That doesn't set a national precedent...yet. If the Supreme Court passes on hearing a case, as they did here, the lower-court ruling becomes the precedent for that appellate district. It is not officially binding on the other districts, but this does give ammunition to folks looking to overturn bans elsewhere.
The Supreme Court tends to take cases when there is a split among the appellate districts, and a pro-traditional-marriage ruling has yet to be appealed up to them. The 6th district, which includes Michigan, is hearing cases as we speak, so they might give that split-ruling that calls for Supreme Court clarification.
It's not a good sign that the case was heard, since there isn't five votes to demand to take the cases. Sometimes, there is another case in the pipeline that they'd rather set the precedent with and will decline to hear a case that would be messier to rule on, but I'm not sure this is the case here.
Today's decision would mean that at least five justices are cool with the status quo downstream, which doesn't bode well for a traditionalist district ruling to stand up. Those would likely be the four liberal justices and Anthony Kennedy, unless we got some odd coalition where one of the conservative quartet sided with the liberals. That center-left quintet would be enough to do the job for the gay-rights backers.