Is the Drake Equation an accurate way of finding the probability of life on planets?

The Drake Equation is a formula for gestimating the number of intelligent extraterrestrial civilizations we might be able to detect, which will most likely be a small subset of planets in the universe that host lifeforms.

Let's see if we can break this down a bit. From the Wikipedia article:

The Drake equation is:

$N = R_{ast} cdot f_p cdot n_e cdot f_{ell} cdot f_i cdot f_c cdot L$

where:

$N$ = the number of civilizations in our galaxy with which radio-communication might be possible (i.e. which are on our current past light cone);

and

$R_{ast}$ = the average rate of star formation in our galaxy

$f_p$ = the fraction of those stars that have planets

$n_e$ = the average number of planets that can potentially support life per star that has planets

$f_{ell}$ = the fraction of planets that could support life that actually develop life at some point

$f_i$ = the fraction of planets with life that actually go on to develop intelligent life (civilizations)

$f_c$ = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

$L$ = the length of time for which such civilizations release detectable signals into space

When Dr. Frank Drake first proposed this formula for estimating potential SETI signals in 1961, very few, if any, of these factors had enough reliable data upon which to form a good estimate. In the intervening decades, astronomers have done much research on the process of star formation. Also in recent decades, a great number of extrasolar planets have been discovered; the massive amount of data returned from the Kepler space telescope is especially helpful when estimating $f_p$. In addition, the developing theory of the Goldilocks zone, the orbital band in which an exoplanet can have water in liquid form, gives us a perspective on the third factor. Thus we are beginning to get some idea of the magnitude of the first three factors.

The last four parameters, however, are entirely speculative. As we only know of one planet which supports life, Earth, and know only one intelligent civilization in the universe, our own, we have insufficient data upon which to form any reasonable conclusions. The current estimates for each factor are summarized in the Wikipedia article.