Is it necessary to ping your sitemap to both google.com and google.co.uk. Or will pinging google.com handle the rest of the google sub-domain sites?
Google.com will handle everything, no worries! Just don't ping too much, they get a little worried when you do that...
If you already submitted sitemap on google webmaster tool, you just need to wait and google will index your site. No need to ping every time you update the site.
if you are submitting any new news post your url here in google: http://www.google.com/support/news_pub/bin/request.py?contact_type=suggest_content