Perhaps the most exciting Herschel project mapping the Milky Way is the Hi-GAL survey of the inner galaxy. This is essentially redoing the Spitzer GLIMPSE/MIPSGAL survey but with greater sensitivity, different wavelengths and in more detail.
The Herschel scientists released a large amount of preliminary data today, including a large swath of the Milky Way in the direction of the constellation Vulpecula as imaged by Hi-GAL. This gives us the opportunity to directly compare the Spitzer and Herschel results.
Here's a Spitzer MIPSGAL image centred around the galactic plane at 59.5°:
You can see this image in the Milky Way Explorer here.
Here's the equivalent preliminary Herschel image:
Of course this rendering of the Herschel data is deliberately overexposed to show the fine detail in the cold dust. The final Hi-GAL dataset will have thousands of luminosity levels and will be able to be rendered in multiple ways.
These results are very exciting - they confirm that Herschel's greater sensitivity will reveal a lot more fine detail in the Milky Way. The full Hi-GAL survey is scheduled to be released in about a year.