I make one request for the linked page's content. I then check to see if the current link supports either and/or both specifications. If I find both, I do a pingback and trackback. I guess maybe I should do only one, but until I decide which is better (and which one to default to at first), I will probably keep doing both. I doubt many blogs will have both implemented.
I've noticed a few weird occurences with the Trackback / Pingback / Referrals stuff.
For example, in this entry I linked to a post on Joshua's weblog, but it didn't show up on his post as a pingback or a trackback. Also, the referrals are sometimes weird - they show up from my main page (http://dotnetweblogs.com/TMarman), for example, or from the dotnetweblogs.com homepage.
Also, I guess it depends on the other person's software, but using both might not be a big deal after all. A link to Greg's weblog showed up as a Trackback for me and a Pingback for Simon, so I know he supports both... but my entry showed up only as a Trackback, not as both. I was going to say how weird it was that my link showed up as one and Simon's link showed up as the other, but then I realized Simon's blog isn't on DotNetWebLogs.com too.... Duh.
Anyways - Scott, to summarize, the pingback/trackback stuff rocks.... :)