I check my filter on my Miele, once a month. Its rare that anything is in there. It takes about one or two minutes of your time. I like to open up the basket on the filter and squeeze some dishwashing liquid on it and then run it under the hot water tap. Close the basket and insert the unit back into the dishwasher. You literally pop it in place and turn and that's it. Its truly no work or no hassle nor gross.
I also just scrape my dishes, you really shouldn't be rinsing them off. The enzymes in the detergent need some debris to work properly.
Before my Miele I owned 2 Maytags for a total of 30 years. They obviously had macerators that ground the food. I would never go back to a North American dishwasher, not ever.

About once a year average -- only if something smells funny (usually turns out to be milk left in the bottom of a glass or something -- once was something stuck in the disposal). I've never had much of anything in the filter, but it's there and can be checked.

In the 3 months I've owned a Miele Diamante, I've checked the filter about every 2 weeks, but there's only been 1 time there was something in there (a small mushroom piece) and that is it. Now I'll probably wait and check it just once a month. It only takes about a minute of your time, so not really a big deal. I'd never go back to a GE dishwasher again!

3 or 4 times a year, about. I wash it out and pull out the stems from flower arrangements or maybe a chunk of busted wine glass. The filters are non-issues.

once a year - maybe.

Like the others, only occasionally - maybe once every 6 months or so.

Wow, thanks everyone - this is much more helpful to know.

I had really wanted a European dishwasher but couldn't find reliable information on how often to clean that sucker!

You guys have me convinced - now I just have to pick which brand and model...

1. Well, I have a Bosch SHXM4AY52N with the filter at the bottom of the pan. I clean it nearly every time I use it. I take them at their word and do not compulsively rinse off dishes before arranging them on the racks. There is usually a lot of water in in the filter receptacle, which holds about 8 ounces. I devoted a turkey baster to the task of extracting all of that. Supposedly it is drained away when a new cycle starts, but I put some food coloring in it and did not see it run across the bottom of my garbage disposal. Possibly I didn't wait long enough. I would not buy this machine again. I would buy one that grinds and disposes of tomato chunks and with luck, doesn't hold 6 ounces of dirty water between washes.

All dishwashers hold some residual water in the pump/sump. What remains is essentially from the final rinse so it's not quite exactly "dirty" water.