Forgive my ignorance on the subject as I am new to it, but am I wrong in thinking that SPF records only were meant to affect outgoing e-mails?

I requested support to add an SPF record to our account and shortly thereafter were received a few emails (on external-domain email accounts ) saying some customers were unable to send us e-mail. In the error message they received back, I find this URL:
http://www.openspf.org/Why?id=snipped_username@seminolecountyfl.gov&ip=64.18.2.133&receiver=208.112.123.72

Is this an example of their SPF record being incorrectly configured?
Thanks.

For a detailed explanation of SPF please see the following page:

http://openspf.org/

SPF will affect any mail sent from your domain, if the recipient server respects the protocol.

Basically it looks as if this domain may be using Postini. If so you will want to either disable SPF checking for incoming email in your mail software or add the Postini IPs to your SPF record so that this does not result in a false negative.

Reference: http://groups.google.com/group/PostiniSupportForGoogleApps/browse_thread/thread/a2338bd9e7b7c045/75be5c182354c4d5

The short answer is

"No, if you setup an SPF record is cannot have ANY effect on your inbound mail."