Value of a Polarizing Filter
Filters are redundant with a digital camera, right? Any filter effect can be reproduced afterwards with Photoshop.
For colour effects, this is doubtless true. It's not true, of course, for a polarizing filter. I think that the two shots below, taken from the same vantage point [harbour, Nanaimo, Vancouver Island, Canada], first without and then with a polarizing filter, show the value of a polarizing filter for sky/water scenes in bright sunlight.
Filters with the Canon PowerShot A700 series cameras
The Canon PowerShot A700, A710IS and A720IS have a bayonet mounting ring, intended for accessory wide angle and telephoto lens. I bought a non-Canon adapter tube (much cheaper!), which allows me to use a 58mm polarizing filter. Sadly, the so-called 'replacements' for the A700 series don't have this feature. I agree with the reviewer who wrote "If this represents a new direction for the A-series then there will be some disappointed customers" [www.trustedreviews.com/digital-cameras/review/2008/09/19/Canon-PowerShot-A2000-IS/p1]. You now seem to have to go up to at least the SX series, if not the G series, to get comparable features.