For this summer I retired my ageing colection of Cokin P filters and made the switch to 4*4 (BigStopper 10 stop ND filter) and 4*6 ND grad Lee Filter sets. Bit of an largish expense outlay, however I am really likeing their consistency and quality!
I did decide to use the Cokin Z-pro holder for the new filters instead of the Lee's own holder that I had some issues with.
My B+W circular polarizers (1 for every lens) remain unchanged, though contemplating a switch to Shing Ray LB's for next year.
Filters remain a very usefull part of photography with digital!
I remember many comments in the past that with digital you no longer needed to use filters and could do everything in photoshop after the capture. However even photoshop cannot recover what is not recorded in the first place, and that is what filters like the polarizers and split nd grads help you capture. .