I went to Mongolia few weeks ago for 20 days, and I have to say that it was a very interesting trip, good experience, specially if you like goat meat, goat cream, goat milk, goat cheese, goat iogurt,......
The best: People sooooooooooooo friendly and nice. Amazing!
Totally recommended if you want to travel to a place which is still fairly "virgin" of tourism, what means that you have the opportunity of being in contact with locals (nomads).
On the other hand, be aware that the fact that this country has not too much experience dealing with travellers, the services (translaters, guides, etc...) can be unexperienced or even a fake. We arranged few services like that (jeep rental, guide,... ) with a guy called Batsaikhan Nyamdash and it was deeply disapointing, messy and time-money wasting. This guy operates as well under the a Travel agency called M.A.T.B. and in few websites. You better stay away from people like that if you want to enjoy travel and arrange everything by yourself, which is pretty straightforward in Ulan baatar as there are many options to do it (students, taxi drivers, local travel agencies,...).
Mongolia is amazing.. I just spent three weeks there myself. All of the guesthouses arrange travel for you but I did work with one I thought was heads and tails above the rest - the one through Golden Gobi guesthouse.
However if you want some good mongolia tips, here are mine.
1) Bring cash or a visa/mastercard you can get it through - as of August the banks were not hooked into international ATMs.
2) Be very aware of pickpockets and random violence in Ulan Baatar - especially for men traveling alone. A number of solo male traveller were met with violence (usually a kick or punch, but one had a bottle broken over his head in a bar) as many mongolian men resent the fact that they were "Looking" at local women (which in some cases they weren't). Couples and groups reported no problems.
3) Pack your own sleeping bag (and tent preferably) a lot of the gear lent or rented in Mongolia is substandard and spending a number of nights freezing because they gave you a sleeping bag unfit for conditions or a tent which won't keep out rain or mosquitos.
4) Don't take advantage of local hospitality - local people will let you sleep in their gers and even feed you, but on the whole they are a very poor people and most don't even have electricity. Things like candles, crayons for the kids, and practical gifts are a nice way to thank them. You may have to "forget" to take it for them to accept the gift.
5) Don't just let the driver of any jeep/van you rent drop you in a place you don't want to be - the drivers get tired after a long day driving (the roads are brutal) and they'll often just take you to the same places that they always go and many of them are so trash strewn and disgusting that you really don't want to camp there. Let the translator/guide know before they start unloading - they do what you want (that's how the treks are supposed to work).
As I am the owner of the agency M.A.B.T Co, Ltd., would like to comment on the barretina's threat.
1) Dealing with travel agency is not same as traveling alone as the agency has the reponsobility of the safety of travelers, thus the request to deviate from the agreed itinenary (which was made by the barretina ) is not possible due to the safety of the travelers.
2) It is always recommended to deal with the professional agents rather than the individual as it is again the matter of safety and quality of the service. Monoglia is an unique destination as it is one of the least densely populated countries with 2.5 mill inhabitats in 1.5 mill. km2 which is less the 2 persons in 1 km2 and almost 40% lives in the capital which make the country side almost empty and no help if you are in trouble.
I would kindly encourage people to deal with travel agencies and arrange everything prior to the arrival or after arrival before the start of the trip to avoid the disappointments and be aware that the local condition is not always predictable and expect some unexpected as part of the adventure in Mognolia and have fun as well.