"I wouldn't advise anyone to start at Khao San. In fact, I'd suggest
that anyone who really wants to see and understand the city should
avoid it at all costs !!!"

For those who don't know, Khao San is basically a street a few blocks
long devoted to backpackers and their various needs. Khao San and its
sidestreets are full of dirt-cheap guesthouses (US$3-5 per night is
common), Internet cafes, discount travel agencies, stalls selling
jewelry, used books, pirated CDs and DVDs, and pseudo-Asian clothing
like sarongs, and inexpensive outdoor restaurant/bars that have Western
food and cheap beer and show pirated DVDs.

Since it's really cheap to stay there and hang out, a lot of travellers
spend several days there while they wait for visas or wait for a flight
out. You will meet people from all over the world (lots of Germans,
Australians, and Israelis especially), but you will rarely meet Thais
who don't work there.

I wouldn't recommend staying there or going there unless you are on an
absolute minimal budget or you want to meet other travellers. There
are far more interesting places and much better hotels, restaurants,
and bars elsewhere in Bangkok.