Regarding Ikea lampholders: Yes, that is exactly the one. Except the ones Ikea sells/sold here used a round SVT cord (round vacuum cleaner type cord with tougher insulation).
Also the lampholder was like the black one you pictured, with the shade-ring but with no switch. I always thought that the reason you didn't put metal screw shells into the sockets was because manufacturers were trying to save cost on metal.
That rocker-switch lampholder is also sold here...it's very expensive - about 6 to 7 dollars depending on the store!!
As far as socket/lampholder adapters are concerned we have a bunch. They come in both brown phenolic (Bakelite) or white urea plastic. I like Bakelite better because it resists the heat and doesn't discolor and disintegrate like Urea does. Here are a few pictures:
Bulb plus two receptacles cluster (may or may not come with a pull chain switch for bulb control only):
This converts a lampholder into a female two-pin receptacle.
This is for plugging a bulb into a standard receptacle or extension cord:
There is also a device for plugging two lightbulbs into one lampholder.
According to UL, the reason why they still approve these devices is that the devices will still be sold/made/imported/used without the approval seal anyway, so they'd rather ensure the device is electrically safe to use (for example the plastic insulator isn't going to disintegrate and separate from the metal components).
How you choose to use these devices is, of course, entirely up to you. You can always plug them into each other and make big weird-looking plastic men!!
Sorry for all the pix and the long post. I just thought you might be interested in seeing some of the crazy electrical stuff sold in NEMA-subscribing countries. I know I love seeing pictures of non-American style wiring devices.
Attribution: All pictures came from LOWE'S website at http://www.lowes.com
(one of those big DIY sheds like Castorama or B&Q or Home Depot)/
[This message has been edited by SvenNYC (edited 11-25-2002).]