Depends really. Are you running the audio to an amplifier?
For me personally, it's not an issue. Am running HDMI cable from DVD player to projector direct and using an optical cable to amp for sound and have not experienced any issues whatsoever
I had a 42" plasma for a week about 18 months ago and this had lip synch problems all over the show. Until I bought it I didn't even know what lip synch was!! Unfortunately I was using an all in one home cinema system and so there was no way to introduce an audio delay to correct this.
I understand that it's largely due to the picture processing that digital displays have to do which delays the picture and the sound obviously doesn't require this processing hence why the sound will arrive first.
I bought a PT-AX100 last weekend and this is one of the questions I've posed myself. Being 'digital' technologies I wondered whether LCD & DLP projectors would introduce a similar delay, and with the image being so big it would be very noticeable. I bought a new DVD player with the projector and this connects via an optical cable to my original surround system. The big advantage of this was that should there be lip synch errors then I could introduce an audio delay box (I was thinking of the Felston 540) to correct the problem.
Anyway, to cut a long stort short, I've already run many different films through the projector & Freeview too and there are no lip synch problems. I'm dead chuffed as this was one of the things I was most concerned about.
Hope this helps!!
n.b. If you are setting your system up from scratch may be worth allowing for either an audio delay box or an amp with audio delay as sometimes it is the source that is out of synch, rather than the delay being caused by your equipment.
You happen to have the projector i am thinking about. I didn't know about lip sync until i saw it on a sky+ recording, so buying anything that could have lip sync problems is a no no. I didn't know there were audio delay boxes either, that could come in handy in the future.