Update (25.1.10): I changed some names, notions that were not used in the right way.
I also changed the usage of SCR (Scan Rate) and made it the equivalent of CTR.
CTR = Clicks/Page Impressions (PI)
SCR = Scans/Page Impressions (PI)

SCR Web Example:
Top-Ad projection per month on http://qrcode.kaywa.com:
441'750 PI's
1'910 Clicks
1'401 Scans
Therefore: CTR 0.4% (0.004) and SCR: 0.3% (0.003), Scan2Click: 0.73

SCR Print Example (open for discussion):
193'601 Print Circulation of a sunday paper in Switzerland
520'000 People read it
950 Scans (first day)
SCR (Circulation): = 0.5% (0.0049)
SCR (Readers): = 0.18% (0.0018)

Update finished (25.1.10):

***

On December 14, 2009, I wrote the post Clicks versus QR Code Scans which I have updated with the latest figures since then.

Here is the short analysis of the two QR Code ads at qrcode.kaywa.com for approximately the last 20 days. Let's first start with the facts (as of today, 13:00 UTC)

Since 11.12.09 on top place, since 18.12.09 on second place
Clicks for Shui Tang Ad: 1'411 – 67 (earlier than 11th) = 1'344*
Scans for Shui Tang Mobile Site (http://m.shuitang.ch/...): 664 – 35 (earlier than 11th) = 629
Ratio Scans/Clicks for #shuitang: 629/1344 = 0.47

Since 18.12.09 on first place
Clicks for #leshalles: 892
Scans for #leshalles Mobile Site: 656
Ratio Scans/Clicks for #leshalles: 656/892 = 0.74

Ratio Scans/Clicks overall: 1285/2236 = 0.57

*If we would be very precise we should only count 1164, as the referrers from bit.ly show that only 1164 came directly via the ad which would give us 629/1164 = 0.54 and overall 0.63. But as we have also published the Shui Tang QR Code on mobile.kaywa.com, we leave it that way.
The #leshalles QR Code therefore is certainly the better example.

Conclusion
Both examples prove and especially the overall result proves, that you can get at least half of the number of clicks with scans – on the Web!

Maybe one can understand now better why Google is so interested in this market. Clicks are there daily bread, Scans will soon become it.