The SERENDIP SETI group is currently conducting search operations on the world's largest radio telescope at the Arecibo Observatory in Puerto Rico. The third generation SERENDIP system, SERENDIP III, is a 4 million channel Fast Fourier Transform-based (FFT) spectrum analyzer with 0.6 Hz frequency resolution. In this talk, we will discuss results of our recent 3.5 year sky survey. SERENDIP has looked at 95% of the sky visible from Arecibo in the range 424 to 436 MHz, analyzed 1.5 x 10^14 spectral bins, and logged information on over 300 million signals. The fourth generation SERENDIP system expands on the SERENDIP III design. SERENDIP IV computes 200 billion operations each second providing spectral analysis on 168 million channels every 1.7 seconds. We will also discuss the design and use of the SERENDIP IV system and future observing plans.