Here is a snippet of my code:
http://jsfiddle.net/natatkinson/xbWEb/

Javascript:

$(document).ready(function () {

    $(#tags).select2({

        maximumSelectionSize: 3

    });



});

HTML:

<form name=form1 id=form1 action= method=GET>

<fieldset>

    <legend>Shoe Info</legend>

    <dl>    <dt>Name:</dt>



        <dd>

            <input type=text name=name id=name size=40 placeholder=Shoe name required autofocus>

        </dd>

    </dl>   <dt>Tags:</dt>



    <dd>

        <select multiple= name=tags id=tags style=width:100%;>

            <option value=0>Select Tags</option>

            <option value=2>racing flat</option>

            <option value=3>track spikes</option>

            <option value=1>trainer</option>

        </select>

    </dd>

    </dl>

</fieldset>

<p class=submit-buttons>

    <input type=submit class=button1 name=submit id=submit value=Add Shoes />

</p>

All that submits is 1 value, not a comma separated list like the documentation says.