[Baalz]

Heh, diplomacy is quite a deep subject that you might have better luck posting in the general forum, but FWIW most people tend to make a good faith effort to follow through with agreements - BUT...

some people just plain don't
some people are in multiple games and forgot what they agreed to
some people have a different opinion on the details of what they agreed to

and finally

Many people are playing for a win so always remember that most alliances will not last longer than they benefit both partners insofar as they're both trying to win.

So to sum it up, you'll have no problem finding reliable allies as long as you're strong enough to have a big stick, but not so strong that you look like you're about to win. Outside of that having high expectations of your allies is just going to be a frustrating experience.

Obviously I speak in generalities, so take it for what it's worth.