I can't give you much of a medical description -- I'm no doctor. But I can tell you that what multiple lipomatosis basically means is "a bunch of lipoma all over the body." In my case, I first noticed them around the age of twenty-five or so; now, at twenty-nine, they're all over my arms and shoulders, with a few around my belly and groin. (I apologize if there's a little too much information here, but I'm trying to be thorough.) They range in size from smaller than a pea to roughly the size of a Sacagawea dollar. Oddly enough, they are often somewhat symmetrical, occurring in pairs on opposite sides of my body.
So far, I've had only one removed -- a very large one on my left leg that was causing me some discomfort when I walked. The lipoma themselves are painless, but they occasionally put pressure on nerve clusters, causing twinges of discomfort or pain. If they get close to the dermal layer, they can also itch like hell. But the only external effect they have on my life is that they make my arms and legs look lumpy... because they are lumpy. Luckily, I'm not vain or anything, so that doesn't matter much to me. There's no way I could ever get them all removed anyway -- I must have several dozen small ones, and a dozen or so noticably large ones.
There is one other indirect problem they cause, though: lipoma are a bunch of benign tumors. This means it may be much harder to spot a real malignant tumor, i.e. cancer. For an anxious person like myself, that's just another thing to worry about.