The hyphen debate will all depend on who you ask, and what they do. But more importantly it will depend on what your search criteria is. In alot of cases it won't matter since you're probably looking for a 2 or 3 word key search, or a cluster.
If you're going to go with a hyphen you have to make sure your supporting text is dead on, and you have a fair amount of experience in ranking. Since a mistake could result in a mis-rank. None hyphen domains are alot more forgiving in my opinion, and experience.
For .mobi I'd say register it and just hang on to it. Right now it's a waste but domain names are not an infinite product, eventually .com,.net,.org names will run out and alternate extension will become more popular and more SE acceptable. But of course that all depends on your predictions on the future of the Internet. ;)
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