I hate the messy spring foliage and trim it back to an inch or so before bloom. The rabbits tipped me off to this, the year they first ate off all the leaves I was annoyed, but when the blooms came up all nice and neat I thanked them. Now I do it every year and the muscari don't seem to mind.
Otherwise they look weedy and unless they're growing in a lawn it's not a look I'm crazy about.

I use mine as a groundcover under shrubs, such as rosebushes. It has not spread at all, because it can't compete with the evil mix of sedum and periwinkle which was there when I got the house. I don't really weed except when I'm redoing a whole bed, and the muscari are actually one of the most weed-free areas of the garden - they seem to be able to hold their own against the hawkweeds and dandelions, which I find impressive. I'd think a border of stones or a railroad tie would keep them in quite effectively because they are so short.

I use them to mark where I've planted other bulbs, thanks to the fall foliage. The leaves have never bothered me - I have low standards. What drives me crazy is digging up an existing bulb while trying to plant a new one. Mine don't seem to spread too crazily, probably because I'd like them to.

I love these but I have the same problem birchhill. Partially my own fault... There is a circle of dirt, enclosed with rocks where a tree used to be (I assume) in my back yard. The previous owner had filled the circle with grape hyacinths. They were nice to see in the spring but my stampede of three dogs... the muscari would soon meet their match. So I dug them up and put them in the front yard (like an idiot, edging the front hedge and bed... so their grassy looking leaves looked like the lawn grass creeping up into the flower beds... not my brightest idea). Then it hit me... they're going to take over. So now I'll have to dig them up later in the summer/fall and find somewhere else for them. Somewhere they can take over without me regretting it and somewhere that they dont look like grass popping up where it shouldn't be. Oye

I spent yesterday digging up an entire flower bed they took over. I have two Costco spinach boxes filled with the little things and have no clue what to do with them. My inclination is to take them out to the back field and spread them. What lives lives and what doesn't doesn't.