Mistifier

The xero : mistifier recreates the hazy, soft-focus effect beloved of traditional SLR photographers. This is ideal for portraits, but can also be used to great effect on landscapes, giving a sort of dreamy quality.

The dialog has two sliders, 'Haziness' and 'Strength'; experiment to find the best settings for any given image.
This portrait of the outrageously beautiful actress Sophie Marceau is ideal for the mistifier approach. The default mid-point settings will usually give a good result for portraits, but here I've raised both settings just a little.
The end result is slightly hazier than I would normally use on a portrait, but shows what the filter is capable of.
On a landscape such as this, a little more mist might be in order, so...
...this is the end result with both sliders set to max-strength. Again, you will need to click the thumbnails to see the effect properly.