What are some good tactical uses for skirmishers? Mine can't charge, and javelins aren't very good weapons. So they shoot sometimes and sometimes do some damage but other than that not much at all. I'm sure there's much better things to do with them than that. Thanks!

I've been using mine to screen my important units so they can close to melee without getting shot by the other sides skirmishers.
We've had 3 infantry units killed in 6 games solely by skirmish units, so they aren't completely helpless, they just need to get lucky.

screening is their main role. Identify your killer Units (for example in a medieval army the Knights) and screen them so that they can charge the target fresh. You can alway interpenentrate the S with all troops so cross them when charging.

As for shooting S can disorder or make casualties to enemy formed troops so your opponent will need to screen his troops. If he doesn't you have chances to weaken him.

There are armies that relies on the fierce charge with troops tha benefit of a high Impetus bonus. For these troops 1 loss in enough to highly reduce their strenght.