SharePoint 2010, how to change column width in list view

Work this CSS into your page:

/* ListView - make Description fields a maximum width and height, and show full text on mouseover*/
/*.ms-itmhover is the TR row*/
.ms-vb2  .ms-rtestate-field{
    max-width:40em;
    max-height:2em;
    overflow:hidden;
}
.ms-vb2  .ms-rtestate-field:hover{
    max-height:none;
    background-color:whitesmoke;
}

You can add a content editor web part to your view page with a content link to a css file containing:

<style>
td.ms-vb2 div[dir='']{
    width:400px;
}
</style>

This will only work if you only have one field on the page that's multiple lines of text (or if you have multiples but you're fine with all of them being the same width).