The specific e-petition forwarded to me is to urge the Government to prohibit discrimination in the provision of goods, services and facilities on the grounds of sexual orientation. (I'm told to ignore the end date and that if you can get to the petition, you can still sign it.) You have to be a British subject to sign it, though.
I have to wonder how seriously any of these e-petitions are going to be taken. But then, do they take traditional paper petitions seriously, either?
I like how the web site explains why they don't have a "sign against" option, saying that you can create a petition for the opposing view. I expect that more people would be willing to "sign against" the petition above than would be willing to "sign for" a petition urging the Government to "continue and promote discrimination...on the grounds of sexual orientation."