Problem 199

Let's take $x=1$, $y=0$ to get $f(0)= \frac {1}{2}$

Method 1: Based on the given $f(1)= \frac {1}{4}$

Take $x=1$, $y=1$ to get $f(2)=- \frac {1}{4}$

Take $x=2$, $y=1$ to get $f(3)=- \frac {1}{2}$

Take $x=2$, $y=2$ to get $f(4)=- \frac {1}{4}$

Take $x=3$, $y=2$ to get $f(5)= \frac {1}{4}$

Take $x=3$, $y=3$ to get $f(6)= \frac {1}{2}$

We can infer that the period is $6$.

Method 2: Take $x=1$, $y=0$ to get $f(0)= \frac {1}{2}$

Take $x=n$, $y=1$, we have $f(n)=f(n+1)+f(n-1)$,

Similarly, $f(n+1)=f(n+2)+f(n)$

Combining these, we get $f(n+2)=-f(n-1)$

So, $f(n)=-f(n+3)=f(n+6)$

Thus, the function is a periodic function with period $T=6$,

Hence, $f(2010)=f(0)= \frac {1}{2}$

So the answer is: $\boxed{\frac {1}{2}}$.

Since the problem asks for $f(2010)$, the term number is quite large, so we can immediately judge that the function must be a periodic function. Therefore, focus on finding the period; the method for finding the period can be either inductive reasoning or deductive reasoning.

Accurately finding the period is the key to this type of problem (where the term number is large). Both induction and deduction methods can be used to find the period. Choose the method you are most comfortable with when solving.