Google Apps users can now purchase additional storage for Gmail, Docs, and Picasa Web... Pricing for this service is the same as for personal Google Accounts.

http://googleenterprise.blogspot.com/2011/03/now-available-with-google-apps-user.html

Why pay $50 per user per year for Google Apps Business and get:

   – 25 GB for Gmail
   – 1 GB for Docs
   – 1 GB for Picasa Web

When you can purchase an additional 20 GB for $5 per user per year and get:

   – 27 GB for Gmail
   – 21 GB for Docs
   – 21 GB for Picasa Web

(Yes, that extra 20 GB is actually shared across the three services, but that still seems like a better deal?)

http://www.google.com/apps/intl/en/group/index.html

http://www.google.com/apps/intl/en/business/features.html

when you buy storage in google apps, you don't get it for gmail