According to the Salesforce.com Edition Comparison data sheet, storage
allotments vary by product edition. Personal Edition users get 5MB per
user. Professional and Enterprise edition subscriptions get the
greater of either 20MB of storage per user or 1GB of total storage.
Unlimited Edition customers receive 120MB per user. Going beyond the
storage limits will result in additional fees.
The storage limits are likely reasonable for structured company and
contact data, however, will fall far short for users with high
transaction volumes or users that want to upload files such as quotes,
proposals, powerpoints, contracts or scanned documents.