It depends... but if your architecture is modular, two unrelated classes should be independent, so that the work can be optimally spread over multiple engineers programmers. As long as your design makes sense and is easily understandable, you can easily scale up to many, many classes. But don't go overboard making a new class for every tiny new thing if it's not warranted, that's where things start to go downhill. For instance, don't make one class for a wooden wall, and another one for a stone wall - they have the same purpose, create a "Wall" class and give it texture attributes and so on. On the other hand, it doesn't make sense to try and fit a wall and a player character in the same class, they are completely different.
For reference, my renderer I'm working on has something like 30 classes (or constructs equivalent to classes), and it is a tiny, insignificant project in comparison to many games out there.
And I don't think it makes sense to ask about expectations here. As long as the game is progressing, why should it matter? Some days you're going to be working hard on fixing and improving one or two classes, other days you might be doing some bug checking over the entire code base.
It depends... but if your architecture is modular, two unrelated classes should be independent, so that the work can be optimally spread over multiple engineers programmers. As long as your design makes sense and is easily understandable, you can easily scale up to many, many classes. But don't go overboard making a new class for every tiny new thing if it's not warranted, that's where things start to go downhill. For instance, don't make one class for a wooden wall, and another one for a stone wall - they have the same purpose, create a "Wall" class and give it texture attributes and so on. On the other hand, it doesn't make sense to try and fit a wall and a player character in the same class, they are completely different.
For reference, my renderer I'm working on has something like 30 classes (or constructs equivalent to classes), and it is a tiny, insignificant project in comparison to many games out there.
And I don't think it makes sense to ask about expectations here. As long as the game is progressing, why should it matter? Some days you're going to be working hard on fixing and improving one or two classes, other days you might be doing some bug checking over the entire code base.
You got a point there. Thanks. 
It depends, its usually 1 class per "real life" object, but sometimes inheritance can add to it further.
So I was wondering, how many classes is a software engineer expected to work with on an average daily basis?
Over 9000.
More seriously, as many classes as the APIs you work with contain. As a (somewhat horrifying) benchmark, Java 7 has ~3,800 documented classes.
There is no right anwser to your original question Warnexus.
It depends greatly on your project. For example, the current professional product I am working on has well over 12.000 classes and more than 25 million lines of code (excluding the generated classes and lines of code).
This might seem a lot, but we are using the SOLID-priniciple, which greatly reduces complexity and improves maintainability. Each day many new classes are created and existing ones are deprecated.
Most classes can be printed on a A4 paper and are very simple in nature. One other advantage is that we get very few merge conflicts and those we do get are solved within a minute.
I've worked on some projects that didn't follow proper OOD rules (e.g. SOLID, mentioned above), so they had a smaller number of classes, but each class had a huge amount of member variables and functions.
On other projects that do use proper OOD, there's more classes, but each one is simpler.
In both cases, the total amount of code that you've got to understand and remember is about the same, so the number of classes doesn't really mean much.
I once overheard a co-worker comparing two implementations of a light-sabre weapon attachment module for our character class, and he was complaining that one of the implementations was complex because it was made up of, like, 3 different classes, whereas the one he liked did everything in a single uber-class. In my mind, all I heard was "I was never taught OOD, can we go back to using C please?" 
There is no number. The number of classes you need is the right number. Every program is different, including games. If you think you have too many objects, maybe you should ask yourself why. Do you feel like each object doesn't perform a unique role? Are there maybe some objects that would be better suited as interfaces? At the end of the day though, there is no such as "enough" or "too many" classes, in general. There is only such thing as "just enough" classes.
