If we are comfortable lecturing ex tempore on a day-by-day basis, over a much longer time period (hour long lectures), on topics that are not always intimately related to our research (we all lecture on stuff we have never written on), to people less patient than scholars (undergraduate students), then surely it is a more straightforward thing to talk for 20-25 minutes to friendly faces on material we know intimately?
Good question. However, part of the problem is (and I don't want to get too political here) the reversal of the power relations at a scholarly gathering. One's students are in a very real way in one's power; if they are lucky, you are a benign, charming, personable, just, and funny dictator. But at a scholarly presentation one is at best among equals, and at worst in front of those who may have something to say about how one's work or reputation may either grow or wither. In either case, the audience has to be won over. If they already know and like you, this will be easy; if not, the work will be harder.
Therefore I wish to question the assumption of "friendly faces." In general, I think one can and should assume basic good will in the audience; however, many of us have seen, during the question period, the spectacle of self-important senior scholars skewering hapless grad students or young scholars just (as it seems) for the fun of it, or because one of their own pet ideas has been questioned. I think that first-time presenters are often intimidated by the presence in the audience of revered or venerable names previously known only from books or journals; and this fear can lead to nervously presented and feebly defended presentations, or to a dogged (and dull) effort to cover all the bases.
Two things are necessary to solve this problem; one is the growth of courtesy on the part of long-time practitioners of scholarship to those entering the guild. Perhaps we have already seen the last of the ritual disembowelings! I fervently hope so. The other thing is the growth in awareness of what we have been talking about: how to make a paper clear, interesting, and compelling.
Does the SBL offer any kind of advice to first-time presenters? It seems to me that this is something its Career Services department could fruitfully address. (Perhaps it already has; I'm coming late to the discussion.)
UPDATE: In reference to Justin's comment below: Dang it, now I've gone and scared somebody. I would just say (a) Don't speak at SBL just to toss out ideas; have something that's a real contribution. Your professors should tell you if you're on to something that's significant. (b) Be aware yourself, as much as possible, of what questions still need to be answered. If someone calls you on it, just say: "You're right; I'm still ironing out the details. Thank you." (c) If someone is mean to you, don't respond in kind. Thank them for their comments, address whatever is substantive in their response, and then leave them to stew in their own bile. Learning to do this is part of becoming a scholar. Finally, let Biblioblogdom know when you're presenting and we'll come and cheer you on.
UPDATE II: Thanks to Jim West, Tim, and Justin for their comments below. Jim Davila adds his thoughts here. And here's a picture of me giving my latest paper.