It depends which data source you consult, for example as of 8/9/2009 here is the data for PAA:
0.49 (Yahoo), 0.38 (S&P)

For comparison here are the Beta data on KMP and BPL, respectively:
KMP 0.27/0.18
BPL 0.2/0.11

So clearly PAA has a higher beta then a few other companies in the MLP gathering/storage space, although you argue that most of these companies tend to have lowish betas overall.

Hope that helps. I have a position in KMR (personally I prefer the PIK model) but PAA is another great long-term holding to consider.