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What's the end goal here? Are you actively trying  to block all bots? If so, I would still suggest "Disallow:/". The other syn-text may also work, but if Google suggests using a backslash, you should probably use it.

You can use wild-cards, in theory, but I haven't tested "?" and that could be a little risky. I'd just make sure it doesn't over-match. Honestly, though, Robots.txt isn't as reliable as I'd like. It can be good for preventing content from being indexed, but once that content has been crawled, it's not great for removing it from the index. You might be better off with META NOINDEX or using the rel=canonical tag. It depends a lot on what parameters you're trying to control, what value these pages have, whether they have links, etc. A wholesale block of everything with "?" seems really dangerous to me, IMO. If you want to give a few example URLs, maybe we could give you more specific advice.

Very nice site. That's some solid onpage optimization and I didn't notice any errors. Some things you might want to consider are authorship markup and semantic markup. Authorship will likely play a big part in Google's algo within the next 5 years, and you get a nice picture in the SERPs which increases CTR. If you have any expert writers that want to build up authority in your space, now is a good opportunity to start doing that. Semantic markup can also help enhance your SERPs, and improve CTR. One piece of markup you might want to start with is breadcrumbs, since you use them on the site. Facebook markup can also help your articles look nicer when they are shared. Social sharing buttons on your articles would be a good idea as well. At least have a G+1 button and FB likes. Those will help with social sharing, provide social signals, give you social proof, and in the case of Google+, help improve your rankings for G+ users.