EDIT: changed the link to "Poor's man wifi" because Google reports malware.
EDIT2: it's worth mentioning that the standing wave ratio using these home-made antennas can be higher than the ratio expected by the device manufacturer.
These returning waves can damage the power amplifier, but with most wireless cards with transmitter power output under 100 mW (IIRC more than that requires a special license in most EU) it's very unlikely (although possible) and it can only happen after continued usage.
Disclaimer: I'm not an expert, just used to play with wireless about ten years ago.
Pringles ones are crap, but I can attest to the power of Illys based antennas, having done one exactly like this for a half mile line of site link to a public wifi hotspot about 8 years ago. Eventually I swapped it out for a sky mini-dish with usb wifi dongle and a small biscuit tin lid as a back reflector, as the Illys can dropped out too much in bad weather.
[edit] Woks with usb wifi dongles are also pretty good.
ie http://www.oreillynet.com/cs/weblog/view/wlg/448
I've always found USB WiFi cards more convenient because you don't need any special connectors (or soldering skills!):
http://www.instructables.com/id/%22Poorman_s-WiFi%22--USB-ad...
EDIT: changed the link to "Poor's man wifi" because Google reports malware.
EDIT2: it's worth mentioning that the standing wave ratio using these home-made antennas can be higher than the ratio expected by the device manufacturer.
These returning waves can damage the power amplifier, but with most wireless cards with transmitter power output under 100 mW (IIRC more than that requires a special license in most EU) it's very unlikely (although possible) and it can only happen after continued usage.
Disclaimer: I'm not an expert, just used to play with wireless about ten years ago.