Neat way of adding active class to cached navigation in Craft - From http://goo.gl/9LaOuM

navigation.twig

{% set navigation %}
{% cache globally for 3 years %}
{% set entries = craft.entries.section('navigation') %}

<ul>
{% nav entry in entries %}
    <li>

        {# Check for entry type / get related entry #}
        {% if entry.type == 'linkedChannelEntry' %}
            {% set linkedEntry = entry.entriesField.limit(1).first() %}
        {% endif %}

        {% if linkedEntry %}

            {# Link to a linked channel entry #}
            <a href="{{ linkedEntry.url }}" data-url="{{ linkedEntry.url }}">{{ linkedEntry.title }}</a>

        {% else %}

            {# Link to a structure entry #}
            <a href="{{ entry.url }}" data-url="{{ entry.url }}">{{ entry.title }}</a>

        {% endif %}

        {# Repeat this for child entries #}
        {% ifchildren %}
            <ul>{% children %}</ul>
        {% endifchildren %}

    </li>
{% endnav %}
</ul>
{% endcache %}
{% endset %}

{{ navigation|replace({('data-url="' ~ craft.request.getUrl() ~ '"'): 'class="active"'})|raw }}