I've read and contributed to many threads regarding GPS uasage in Europe but I don't recall this being asked:

Is it legal to bring my suction cup device to window-mount my GPS? Here in the States California supposedly forbids this, but it seems to be ok everywhere else. Since the Europeans are often a lot more restrictive about driving rules, are there any regulations regarding the possible obstruction of vision by window-wounting my GPS? I've take my Garmin Nuvi on four trips in the past but just laid the unit on the center console. With my last van rental I found it very difficult to look at the maps on the GPS laying down there. Obviously I don't want to install a permanent holder in a rental vehicle.

My husband has a bean bag type device for mounting GPS and placing on dash. Very convenient and it doesn't fall off. Everyone who has seen it has wanted one. I think it's called a Garmin portable friction dashboard mount.

Each country has its own laws so it depends where you are going. I've never heard of these cups being banned anywhere, but that isn't to say that they aren't.

Anyway, in UK, no problem.

My husband uses a suction-cup GPS holder - he bought the first one (which broke) here in Belgium and got a new one in France. As far as I know there are no rules forbidding them...

We also have the bean bag device for mounting our Garmin Nuvi in rental cars. Used it in Canada and Europe last year. Agree with luvtravel that it works great.

There is no legal reason why you can't uses a suction cup GPS mounting as long as they don't obstruct your view, obviously. You will see them extensively. A word of warning though. I strongly advise that you unclip the GPS set and 'unstick' the suction device whenever you stop, including service stops on motorways. They have become the car thief's object of choice here in the UK for the last couple of years, and I suspect the rest of Europe also. There have been many examples of cars being broken into due to those grubby circles left on the windscreen by the suction cup, so be wary.

The Garmin friction bean bag thing is excellent (if you have a Garmin!). I have just returned from a trip from the UK to Austria and used one with my handheld hiking set on the dash, as well as a TomTom and one already integrated into the car, but then I like toys.

A final point to bear in mind - Both the TomTom and the car's own system (Trafficmaster) came out with rubbish a few times during planned routes so have some idea of where you want to go in your head and have a paper map as a back-up.

They are allowed in the Netherlands - but the recommended place to stick them is the top left hand corner of the windowscreen to avoid obstructing your view. There have been a couple of cases here of people being prosecuted for having one on which did obstruct their view, though the chances of that happening to a visitor are negligible.
The ring left on the screen is as stfc says a target for thieves. They realise most people remove the GPS from the screen, only to "hide" it in the car.
Both Garmin and TomTom have beanbag type devices.

Here in Spain they are allowed but you must not reprogram whilst driving and the screen must not obstruct your vision. However you are not allowed DVD screens in the front of a vehicle.

Zeus : I noticed elsewhere a post of yours mentioning using a GPS to get to Cesky Krumlov. In December we are renting a car in Frankfurt, driving to Prague via Rothenburg and CK. I have a GPS in my own car and think having one for travel would be terrific - if the maps are bang on correct. You mentioned being guided onto narrow backroads I think you mentioned a Garmin Nuvi. I am considering buying a GPS for this trip Would you recommend the Garmin ?

It is NOT lawful to use suction mounted car cams or GPs units in the UK or EU

English Law - The Road Vehicles (Construction and Use) Regulations 1986
European Law - Automotive Directive 77/649/EEC

If you do, you can get fined. If you are involved in an accident, you could face prosecution for driving without due care or attention, or even dangerous driving. If you are involved in an accident where someone dies, you could be prosecuted for death by dangerous driving (2 year jail term). These things will fail your MOT and render your car insurance invalid.

Galiano, I have a Magellan GPS which I used to use in Europe but on the last trip I used Garmins in both my rentals (Germany and Italy) and they worked great, including speed camera warnings. I was very pleased with their performance. I would not buy one unless I thought the cost of renting one was going to be more than buying one AND I thought I would use it a lot at home. All my vehicles at home have built-in units now.

vCam, which bit of this act applies? GPS wasn't around in 1986?

Using those GPSs is of course legal. In Switzerland you may get into trouble if trffic police sees it. It's not legal to use any type of speed camera warning system in Germany and will be fined including penalty points, if they ever catch you. A GPS device must dispay a warning that you break the law if you activate that function. LOL! Those things are sold in France, where it doesn't seem to be a problem at all.

To begin with I am unclear why vCam resurected this old thread.

The laws vCam refers to are for visibility through the windscreen aimed mainly at vehicle constructors.
Strictly speaking it is correct that a sat-nav on the screen is illegal, since it reduces visibility. There have been some cases of people being prosecuted for badly positioned sat-navs, but generally provided you don't have the thing slap bang in the middle of the screen you will not be prosecuted, and your insurance certainly won't be voided.
A UK tax disc is equally illegal since it covers part of the windscreen but you are more likely to be prosecuted for not showing that than for showing it. Most sat-navs don't cover much more of the screen than a tax disc.