Gosh, what would you like to know? It's one of the nicest places we've ever lived and we've lived all over the US and the world. It's located in the Skagit Valley and when you drive down into the valley on I-5, for us, we breathe a sigh because of the beauty and because we're fortunate enough to call it home.
It is a rural community with much agriculture taking place. It allows for Sunday drives

to roadside outlets for flowers, honey, vegs, fruits etc. The famous Tulip Festival is just about to start next weekend.
The other posters have given some good info and you can add to what you know already by going to City Data's city info for Mount Vernon. They have lots more information and some great photos as well.
I wouldn't say that the cities of Mount Vernon/Burlington are small by any means. They are separated by a bridge only. There is a decent population (26,000 from City Data's stats) with schools, shopping, churches in abundance. There are all the major retail chains, there is an Outlet Mall and Cascade Mall and tons of restaurants as well. It is very progressive with lots of new shopping outlets being added in the last few years. It has a feeling of "new" rather than "old".
True, there are the older parts of the city but there isn't much shopping that anyone does there perhaps with the exception of the Co-operative where you can get organic foods of all kinds.
There is a large and (getting larger) hospital with doctors and all kinds of medical needs taken care of right here in town. And the Skagit Valley College is adding buildings as we speak which is great for the students who have been doing with cramped conditions for too long.
It's also only about 20 minutes drive from Bellingham where there is lots of other shopping, and the Canadian border is only about 1.5 hours drive away.
Added to that is the beauty of the area. We are situated between the Cascades and the Olympics (across the Sound) in the far distance, but much closer to the Cascades. Mount Baker isn't that far away for those who like to ski or snowboard like my son. All in all it's a great place to live.