I have a mix of PLO8, NLO8, and limit O8 tourneys in my db. When I filter by limit or PL it's obvious that the number of tourneys showing isn't changing. If I dig down to see how the tourneys themselves are stored (in Data View), it's obvious they're marked as L, PL, or NL appropriately.
I did find this old thread that appears to indicate that it worked at one point. I haven't been importing PS summaries in a while because it's kind of a hassle but the filter doesn't seem to take effect for Full Tilt tourneys either. At any rate, the L/PL/NL info is plainly importing correctly.