Texas has a state constitutional amendment forbidding same-sex marriage. Virginia has a constitutional amendment banning both same-sex marriage and civil unions.
The Illinois constitution, sanely, is silent on the issue; every year we get closer to passing a same-sex marriage law; it's a foregone conclusion.
In general it's nearly useless as a constitution, in the sense of a stable document setting forth some general principles. It's been amended 474 times! So it's more like a giant grab-bag of legislation. That's usually bad, but in this case good (if you support SSM), since it's not set in stone.
The bigger issue isn't the structure of it being in the constitution, but the fact that supporters of SSM can't currently get within striking distance of 50% support in the state.
I can't imagine it'll be anything but a good thing for these companies, ultimately.
The biggest tech centers are now all in SSM-supporting states; TX, VA, CO, IL, and NC seem like the most important holdouts.
However, they only struck down the federal part, not the requirement that states recognize each other, so there's still a strong incentive to stay in an SSM-ok state even after marriage in an SSM state.