I went with my wife on an Exodus holiday in 2007. Landed in Beijing and transported to Chengde ~ 200 miles NW of the capital and then spent 2 weeks cycling back towards Beijing.
We were cycling through villages that had never seen a westerner before, it was fantastic. Yes I ate some strange things, (dog, donkey, thousand year egg....), and got the runs one day, but overall it was an amazing experiencen that you have to jump into. If you can learn some basic chinese it will go a long way, even just saying 'hello' (pronounced 'nihow') will bring massive smiles to their faces.
We walked along 3 sections of the wall, the most spectacular being the Jingshanling to Simatai section. It's a steep treck at times but it's the classic wall section that literally follows the ridge of the mountains.
Other highlights were the Qing tombs, NW of Jixian, real 'Raiders of the Lost Arch' kind of stuff.
Within Beijing, there's the normal well known stuff, but also search out the series of underground tunnel tours that were once the nuclear fall out shelters during the cold war, really interesting.
Also get tickets for the Chinese acrobats/Circus, it's a permanent show in a theatre in the east of the city, (sorry can't remember the exact location or theatre name). It's ferkin amazing, you wouldn't believe a human being could do things like that!!
The Olympic birds nest stadium is also worth a visit plus the chinese markets near the circus theatre.
You will get constantly hassled in Beijing by street sellers, but there are bargains to be had if you do want a bootleg Rolex, Brietling watch etc etc 
I got two for £20 and they are top quality, with full automatic movements and have kept time for ~4 years now 
As mentioned above, going to the toilet is a social event, especially in public places. It will literally be a line of holes in a concrete slab and the chinese men are not shy at checking your equipment out 8O. However, you will be relieved to know they are not too well 'blessed' in that department so even an 'average' westerner can swing it about a bit with pride - ha!! Try to save any 'big jobs' for the hotels which generally have normal type cubicles and you will be ok.
My wife is tall and blonde so she obviously was the centre of attention wherever we went from both men and women, although my ginger hair did cause some ammusement and I was once called an orangutang - ha!
