We almost went w/Alder but when I tested it I found that it was easily dinged. I was originally going to use it as a substitute for Cherry since they are similar in look. The Cherry was a 20% up charge and Alder was no up charge. In the end, we decided to go w/the Cherry as I realized that it's not just the kids who ding things, but when I put things away I sometimes bump a door or frame or when I'm moving around in the kitchen w/broom or mop.

If you're going for a rustic or distressed look it may be fine since dings will blend in. However, if you are someone who likes things pristine and you'll constantly worry about it, I would think twice.

I did knotty alder in my new laundry room and the first thing my DH said is that he would never do them in our kitchen. The wood is too soft. I would only even consider knotty alder in a kitchen if I had NO kids or pets and would baby them. Like Buehl, I went with cherry and had the wood distressed. There is a very noticeable difference in the hardness. Yes, it was more expensive, but I think worth it.
The knotty alder cabinets are beautiful though!
I will post a link to my laundry cabinets.

Here is a link that might be useful:

I'm considering semi-knotty alder. My cabinet maker is going to request less knots. I was worried about this too, so my cabinet maker is also getting me a beech sample.

Either way, I've now spoken to three cabinet makers who say that they install lots of alder cabinets in kitchens, and have yet to have a complaint, or have people change their minds once they get a sample.
They also said that a vertical surface isn't going to take the damage that a horizontal surface will take. I had pine in my last house and it's about as soft as alder. I had no problems with that at all.
Of course, here in the south, cypress is also a real popular wood for cabinets, and it's soft like that too.