I know a retouch guy who is so fast at this it's untrue. It's a case of practicing with the pen, mask and selections tools.

I'd say decent product shots are very important - typically it takes me a couple of minutes or so to get from import raw to export JPG - but it does depend on the complexity of the item.

A couple of tips for speeding up things:

Shoot the product using backgrounds to match the website. A quick level change, selection, crop and resize can be all you need then.

Rather than erasing or filling backgrounds it's better to use clipping paths IMO

Save all source PSD files with masks and clipping paths in place

Work at high resolution so the images can be used across media

Save actions for resizing your images and exporting to JPG.

How long would you spend in say Photoshop clear cutting or background erasing an image to use in a product catalogue on the web.

Hard edged items - from 3-7 minutes depending on the complexity. When hair is involved, it depends on how good you want it. For a seamless convincing job with no short cuts, it can take up to an hour. Usually in this case I'll get all the hard edges in and the hair roughed out, then switch to mask mode and us the airbrush/eraser with a Wacom table and varying degrees of opacity (on the mask) for a "perfect" job.

How important do you consider it to get it "perfect" getting rid of artefacts, poor edges etc.

Very. The buzz on all the message boards is "good Photochop" meaning anyone can do this, but doing it well is another story. You can spot the signs of a auto-select and identify filters instantly. :-)

Rather than erasing or filling backgrounds it's better to use clipping paths IMO

For print, absolutely, especially when the layout person may want to resize or impose over other elements in a layout program, but I find clip edges far too unnatural for image-on image work. <shrug>

Work at high resolution so the images can be used across media

Generally I find I get better results if I size the image first and knock out later. It tends to lose a little character sometimes if you scale down an original that's already knocked out.

There are several ways to do the same thing in Photoshop. I would use the tool that can cut out the main image from a background and then save the resulting image to its own file for later use.

How long? - I guess as long as it takes (you).

"Perfect" is a relative concept, I think....
My 10 centimos

I just spent the last month cutting musicians out of various backgrounds. After a little practice with the pen tool in photoshop, it takes me about 10 minutes to cut out most backgrounds. (if hair or feathers are involved, add about another 10 minutes or so).

At least, that's how it works for me.

Combination of hardware/software/image. Good strong hardware (speedy) + software + clean image = QUICK. Muddy or busy images will take longer. Product images are, generally, fairly clean unless they have text/etc you want to remove. As long as the text is not on the product, a quick wipe at near same color of background is done, then use the paint bucket in color select background at about 32% to fill. Done. Most of these take about 2-3 minutes.