Well, I suppose a null vote is still a vote. I don't see much need for any of those suggestions. As has been pointed out, most people have the ability to spell-check, they just don't, or their spelling is so bad (we can generously assume it's because English is not their first language) that spell-check can't suggest anything useful. Besides, spell-check can't tell you if you have the right word, which is usually more important to clarity than a slightly mispelled one.
As for study groups and quizzes, I'm a bit beyond that stage of my life. I'm not sure how study groups would work here anyway. Would those be set up through a chat feature? Having led several study groups, I don't know how those would work when people aren't all in the same course covering the same material. I'm also a big fan of visual aids, so really don't know how that would work out here. But, like I said, I'm well past that stage of my life.
I already have personal weather on a number of other sites I visit, so really don't need it here too. Now, if it displayed a 5 day forecast without having to follow links, I might be interested. Most sites just display the current weather, which I can more accurately obtain by looking out the window.
A science glossary...hmmm...now that I've eliminated everything else, that sounds reasonable. I don't know how much I'd use it, but it seems like something that would be helpful for some people who get bogged down when limited understanding of technical terms prevents them from fully participating in a topic, especially if they have a LOT of questions of that nature that people get tired of answering them. I started out thinking that there's one of those in the back of every textbook, but I forget that this is the electronic age when people don't like the idea of dragging out a 1000 page text to look up a word, and not everyone has relevant textbooks on hand. So, I think I'm going to go check the science glossary option.