I never had a problem with wearing a tie, and a full windsor knot (not the wimpy half windsor most techies use, when they have to) looks pretty good if the tie isn't too wide. The problem is that people don't wear neckties much any more -- in my job or even at church -- so I pretty much had to give up wearing them most of the time.
Wearing a necktie at a formal (or even semiformal) gathering -- many of which include food -- might provide a situation where I might spill on it, but that's typically not a lunch event.
Keep in mind, however, that spilling something on tye at lunch might land you in the Belly of the Borg :)
Update, 27-Sept Went out to lunch, didn't wear a tie. Spilled contents of my burger, and now have to deal with a stain on my pants (trousers, for those of you in the EU). *sigh*