URIBL not as effective as it was

[Paul Welsh]

This time last year I could rely on the URIBL family of anti-spam measures
within spamassassin to detect loads of spam very reliably.  Examples
include:

URIBL_SC_SURBL
URIBL_AB_SURBL
URIBL_WS_SURBL
URIBL_SBL
URIBL_OB_SURBL
URIBL_WS_SURBL

Seems to me these are far less effective than they were (they aren't showing
up as much).  Can anyone confirm this from their own experince?