I just bought a 910 from Bud's for $399 shipped, brand new with 15 round magazines, and took it to the range Thursday. Shot like a dream. I've owned other 3rd Gen alloy frames and all seemed to wear well. They do get a little bit of polishing along the frame rails, but not enough to be of any concern. Actually, after they get broken in, they seem to stop wearing. Shoot better then, too. I would think they could take thousands of rounds without having any problems.
They are a little different than the 59XX series, though, in that S&W doesn't spend the extra time on the finishes. There's definitely a difference, however the value lines are plenty acceptable. Also, they have a few plastic and MIM parts that their more expensive counterparts don't. If that's worrisome to you, I believe you can swap them out for the better pieces, although I don't really think they're necessary.
So far, with about 150 rounds through mine, I'm very pleased. I got a nice little tack driver for a sweet price. A very accurate shooter that almost tells you after every round that it hasn't even thought about jamming. She'll like it, it's heavy enough to handle like a .22, but still light and small enough to fit nicely in a purse. I could carry it as easily as any of my Glocks. Additionally, it's about as easy to clean and maintain.