It's been a while but I believe when using the "Send mail as" feature in gmail it puts your preferred address in the from: field but keeps your gmail address in the sender: field.

That's probably fine in most cases but I was getting inconsistent results when people replied to my emails. Some were addressed to my domain and others to my gmail address.

I was also concerned that this might give me a slightly higher perceived risk in some SPAM filters.

Like I said earlier, none of this was a huge deal. It was just one of those inconsistencies that led me to routing all my mail to Google Apps.