SPSS v19 may indeed have better "functionality", (wtf?) and I'll bet that its graphics are indeed better, (PSPP's histograms and pie-charts are somewhat basic). But for the moment it can do everything I need, which is crunching lists of test scores and establishing mean, mode, median, skewness, kurtosis, range, standard deviations, etc., and, most importantly, correlation co-efficients.
But it's not perfect. There is an occasional bug, the cause of which I haven't isolated yet, (though I probably can when I get time), and the basic graphics might be disadvantageous in non-academic, commercial situations. The bottom line though, it's open source, free, and easy to use. The latest version of SPSS can do more. But it can't do enough to justify the cost - which is £200 for a student edition.