Question: As I understand, an object with mass cannot reach the speed of light because its (relativistic) mass increases "exponentially" as it approaches light speed.

So there is a relation between mass and speed. But if speed is a relative measurement (it depends on a point of reference) how does that affect the mass?  

Is the mass also relative to a point of reference?  

Or is there some absolute speed (wrt some fixed point) which affects the mass of an object?

***Follow-up***:  

What I have trouble to understand is... given these two facts (I hope I got the facts right):

1. Light always moves at the same speed (independently of the inertial
frame of reference)
2. The speed of a mass object is relative to a frame of reference

then if an object is moving at 99.999% of light-speed for a given observer, what will a different observer see?  

Will that other observer see the object moving at a different percentage of light speed?  

(assuming the observers are moving at different speeds, of course)

Answer: 
According to SR, an object's *momentum* increases without bound as $v \rightarrow c$

$$\vec p = \frac{m\vec v}{\sqrt{1 - \frac{v^2}{c^2}}}$$

and indeed, an object's momentum is frame dependent.

However, an object's *[invariant mass](http://en.wikipedia.org/wiki/Invariant_mass)* $m$, (a Lorentz scalar) , is *not* frame dependent.

And that's all that really needs to said about that.
> 
> The speed limit is with respect to what?
> 
> 
> 

Speed is relative - this means that you have to specify which frame an object is moving with respect to. So the speed limit is with respect to whichever frame you are talking about.

E.g., Two spacecraft are moving in opposite directions at $\frac{2}{3}c$ with respect to the Earth. With respect to one of the spacecraft, however, the Earth is moving at $\frac{2}{3}c$, but the other spacecraft is *not* moving at $\frac{4}{3}c$. It is moving at a speed given by a formula called the velocity addition Lorentz transformation. The need for this Lorentz transformation arises at speeds comparable to c, due to the fact that objects travel through spacetime at a constant rate.