leonmarino! Great minds think....at the same time!
You can certainly get your shinkansen tickets in advance; there's nothing wrong with that at all. I personally don't like to hassle with buying shinkansen tickets in advance, but to elaborate on my previous post, it's only been a problem so far when I tried to take the last shinkansen for that particular Sunday (it was always a Sunday night) from Osaka that would get all the way to Fukuoka. Other than that, I've never had a problem obtaining a reserved ticket.
And in all fairness, at that time, I was too cheap to ante up the extra 500 yen required for a reserved seat, so I didn't even try.