I guess we should not be surprised that conservatives are looking for niches in Obama's armor to try and shoot an arrow through to injure him. When you have an ideological enemy, that's what you do. The left certainly tried to do it with the many odd Bush behavior traits.
And of course, Obama's manner of speaking extempore lends itself to criticism, because it is fairly slow, cautious, and full of fairly normal 'filler words' and stutters. Partly that's because he doesn't want to respond with answers that are glib or superficial, and I like that.
Here is James Fallow's take on this issue:
Obama's opening statement at this evening's press conference, delivered no doubt with the help of a teleprompter, sounded smoother and more polished than his real-time answers through the rest of the event.
The same is true for any public figure who has learned to use a teleprompter (harder than it seems) and whose teleprompter-ready material suits his or her natural speaking style. It sounds smoother than extemporized speech because it should be smoother.
The important point with Obama is that the content, command of fact and concept, and overall intelligence of his extemporized answers matched that of the scripted presentation. That could not have been so if he were teleprompter-dependent.