This is PubCenter basics

PubCenter is Microsoft's ad platform for web and Windows Phone which competes with Google's AdMob. They differ in the approach used to calculate the revenue. PubCenter is impression based which means that the user only needs to see an ad. The user does not need to click on the ad in order to generate the revenue.
AdMob takes a different approach. It ignores impressions. The user needs to click on the ad in order to generate the revenue. AdMob's advantage is its global reach and availability. It is available virtually in all countries. PubCenter is fairly limited
Developers with a residence in these countries can open a PubCenter account and receive a payment from Microsoft:

1. Australia
2. Austria        (coming soon)
3. Belgium
4. Brazil          (coming soon)
5. Canada
6. Chile           (coming soon)
7. Colombia    (coming soon)
8. Czech Republic  (coming soon)
9. Denmark     (since 2/1/2012)
10. Finland
11. France
12. Germany
13. Greece        (coming soon)
14. Hong Kong (since 2/1/2012)
15. Hungary      (coming soon)
16. India           (since 2/1/2012)
17. Ireland        (coming soon)
18. Israel          (coming soon)
19. Italy
20. Japan           (since 2/1/2012)
21. Luxemburg   (coming soon)
22. Mexico        (since 2/1/2012)
23. Netherlands
24. New Zeland  (coming soon)   
25. Norway
26. Poland          (coming soon)
27. Portugal        (coming soon)
28. Singapore     (coming soon)
29. South Africa (coming soon)
30. South Korea  (coming soon)
31. Spain
32. Sweden        (since 2/1/2012)
33. Switzerland   (since 2/1/2012)
34. Taiwan          (coming soon)
35. United Kingdom
36. United States

Developer supported countries do not equate to ad support for the same country. PubCenter ads are served only to devices in the following countries:

1. Belgium "nl-BE"       (since 10/11/2011)
2. Canada "en-CA"
3. Denmark "da-DK"    (since 2/1/2012)
4. France "fr-FR"          (since 10/11/2011)
5. Germany "de-DE"     (since 10/11/2011)
6. Hong Kong "zh-HK" (since 2/1/2012)
7. Italy "it-IT"                (since 10/11/2011)
8. India                         (since 2/1/2012)
9. Japan "ja-JP"             (since 2/1/2012)
10. Mexico "es-MX"       (since 2/1/2012)
11. Netherlands "nl-NL"
12. Spain "es-ES"           (since 10/11/2011)
13. Sweden "sv-SE"       (since 2/1/2012)
14. Switzerland               (since 2/1/2012)
15. United Kingdom "en-GB"
16. United States "en-US"

PubCenter has a limited use for international apps because of its restricted availability. Therefore, the best approach is a hybrid one. Use PubCenter if the user is in a supported country and fallback to AdMob if the user is located in any other country. A Silverlight user control that handles that automatically is called AdRotator. Besides PubCenter and AdMob, it also supports AdDuplex.

Payout 

Payout is calculated once a month. The payment is sent electronically to registered bank account if the developer's PubCenter account balance is at least $50.

Update 1/27/2012: Added 7 new countries where ads are served. Added 7 new countries where developers can receive payments.

Update 6/11/2012: Added 17 new countries where developers can receive payments.