Steve,
Love some of your flickr images.
Afraid I'm only starting out and limited experience with filters but can share what I've experienced so far.
I got the Hitech Grad NDs and took these :
http://www.blipfolio.com/simonB/weather#m6-sunset--1
http://www.blipfolio.com/simonB/weather#m6-sunset--2
(link doesn't seem to work too well so just navigate to find the motorway/sunset images
For my 1st attempt I was jumping with joy. (although you can see the grad line, oops)
However, the sky is much redder than it was to the eye .. I was stacking a 0.3, 0.6 and 0.9 ... and colour cast was definate.
With it being graduated, you can't PS rectify the result.
I percevered, but soon got fed up with ALL my landscapes having the same cast.
Returned them to supplier for a full refund. (advertised as 'aboslutely' no colour cast).
I can't afford it, but ordered the LEE holder and a lesser number of grads.
It was either photgraph with something that will do the job, or don't use filters at all.
Only had 1 outing with them, my fault I shot badly so crap results, but NO colour cast and the filters did their part of the job brilliantly.
Useful info maybe :
The LEE softs are MUCH softer than the Hitech ones, when used on my 400D. Very soft.
The hards are seemingly much more useful 'to me' so far.
That all might change as my eye becomes more aquired with experience, but for now, I'd go for hards.
Hope that helps a little.
Yes, scarey money ... but it was either that or be frustrated with my landscape results for the next 5 years.
