For what it's worth, I just picked up the XDm (in .40) but did shoot the new XDm 9mm as well and I've gotta say, they're both very nice. The XDm's just fit my hand like a glove (easy to hit the mag release button and slide release with my thumb without having to stretch my hand or reposition my grip on it.) From what I saw, they're also priced very close to the XD lineup and I figured the extra capacity alone was a worthy reason to go with the XDm. Throw in the buttload of accessories SA throws in with any of the models (two mags, mag loader, basic holster, chamber lock, cleaning brush, sexy case, etc.) and it was a no brainer for me. The XDm, for me, beat out the H&K USP (including one of the 9mm versions, the .40, and the .45 tactical) which is hundreds more in price.
The stories I've heard about their customer support (think Logitech/Newegg levels) and the two free mags promo sealed the deal for me.
1st time gun owner here though, so take my love of the XD/M lineup with any applicable grains of salt.