The WaPo has this editorial with some refreshing evenhandedness regarding Supreme Court Justices appearing at events with their expenses paid by the organization.  They note that Justices Scalia and Thomas have been criticized for such events at conservative organization but Justices Breyer, Ginsburg, and Sotomayor have done the same at events sponsored by liberal organizations.

The WaPo's bottom line is that they think there is some appearance of impropriety in this and suggest that the taxpayers pay the expenses.  On that point I disagree.  There is nothing at all wrong with inviting someone to speak and just reimbursing expenses with no net profit to the speaker.  I have been a guest speaker at such events, and it is definitely not a vacation or a benefit to the speaker.  Preparing for the event, traveling to the event, and speaking at the event is work, and the travel expenses paid by the organization are rarely greater than the value of the speaker's time.  Only once in my experience, for an overseas trip, has the value of the trip even been close to the value of the time.

In nearly all cases, it is clearly a matter of the speaker doing a favor for the organization, not the organization trying to curry favor with the speaker.  This is much ado about nothing.