Yes, always say you are new. When I see that I take the time to explain. As WHM primarily, sometimes I'm mid-typing a boss mechanic explanation and the tank runs on in :P
But, hey, I finish the explaination and heal while i do, if i have to.
I'm levelling my tank now, and wierldly, doing Tam-Tara 4 times this week with other people, NOT new, I always take the left corridor at the split and all 4 times one of the members got the mapping achievment. They were happy (and surprised)!
Also, when i got Satasha on LLDR, there was a newbie and I asked at the big room section "All rooms for xp, or straight through?". The newbie wanted xp (and the others were cool with that). In the last corner one of the lv50 synced got the mapping achievement!
So, yes, they all definately got rushed through on their first time!

I like to meander...