Solution:
(I) From the problem, we know that $f(2^{2}) > 2= \frac {2+2}{2},f(2^{3}) > \frac {5}{2}= \frac {3+2}{2}$, $f(2^{4}) > 3= \frac {4+2}{2},f(2^{5}) > \frac {7}{2}= \frac {5+2}{2}...$
From this, we can draw a general conclusion: $f(2^{n+1}) > \frac {n+3}{2}$. (Or we can guess $f(2^{n}) > \frac {n+2}{2}$ $(n\geqslant 2,n\in\mathbb{N})$ is also valid).
(II) Prove by mathematical induction:
(1) When $n=1$, $f(2^{2})=1+ \frac {1}{2}+ \frac {1}{3}+ \frac {1}{4}= \frac {25}{12} > \frac {4}{2}= \frac {1+3}{2}$, so the conclusion holds.
(2) Assume when $n=k$ $(k\geqslant 1,k\in\mathbb{N})$, the conclusion holds, that is, $f(2^{k+1}) > \frac {k+3}{2}$,
then, when $n=k+1$, $f(2^{k+2})=1+ \frac {1}{2}+ \frac {1}{3}+…+ \frac {1}{2^{k+1}}+ \frac {1}{2^{k+1}+1}+ \frac {1}{2^{k+1}+2}+…+ \frac {1}{2^{k+2}} > \frac {k+3}{2}+ \frac {1}{2^{k+1}+1}+ \frac {1}{2^{k+1}+2}+…+ \frac {1}{2^{k+2}}$,
$> \frac {k+3}{2}+ \frac {1}{2^{k+2}}+ \frac {1}{2^{k+2}}+…+ \frac {1}{2^{k+2}}= \frac {k+3}{2}+ \frac {2^{k+1}}{2^{k+2}}= \frac {k+1+3}{2}$.
Therefore, when $n=k+1$, the conclusion also holds.
In summary, the above conclusion holds for all $n\geqslant 1$, $n\in\mathbb{N}$, so the conjecture is valid. $\boxed{\text{Valid}}$