There are several areas to pay attention to in Magento Admin:

Configuration in Magento

You can find this page under "System > Configuration > Salesforce > Customer"
Default Owner is set to "Some Guy". Now, what does that mean? It means that if a customer registers on your website (or places an order) and IF this customer DOES NOT exist in Salesforce at all (based on the email address). We will create a new Account and Contact in Salesforce and "Some Guy" will be the Account+Contact owner by default.

Customer Record in Magento

• There are two places where you can set an owner FROM Magento.
  Contact Owner can be set / changed from "Account Information" tab in Magento (see below)
  
• Account Owner can we set / changed from the "Salesforce" tab in Magento (see below)
  

Order Record in Magento

• Order owner (or Opportunity and Order owners) can we set / changed from Magento Admin panel from two locations:
  From the Order View > Information tab
  
  
• From Salesforce tab
  

Summary

• Your system is configured to use "Some Guy" as a default owner for NEW Accounts or Contacts
• Your System is configured in a way where Magento will ONLY set a record owner when creating a NEW record in Salesforce, record owner will NOT be updated from Magento anymore. (see various mapping pages and "owner" field (M > SF should say "Insert Only", which means Salesforce will be the system of record to track a record owner)
• You SHOULD train your staff to set their name in the Order or Customer records in Magento when creating new orders or creating new customer records. If this practice is adopted, you can safely let Magento be the system of record for the owner field.