Yes, they came to my home when I'm not there. 2 african national with flip-flops sandal entered the villa gate, knock the door so & so...
No sticker affixed on the gate, no original identification on them. You can see the detail here: http://www.qatarliving.com/node/574374 & http://www.qatarliving.com/node/537862

Here are the links from official site:
http://www.qsa.gov.qa/QatarCensus/
http://www.qnaol.net/QNAEn/News_bulletin/News/Pages/09-06-02-1516_263_00...

It is said there:
"According to the officials, the enumerators involved in the census have been enrolled in 3-day intensive training programme and equipped with the latest technology tools that help the authority achieve effective results. "The census methodology has been carefully designed to ensure accuracy of data and will help QSA to develop effective tools and methods for the forthcoming general population census in 2010", said the official."

"Qatar Statistics Authority calls on all families, individuals and owners of establishments to provide full cooperation and support to the census enumerators, due to the significance of the census. Enumerators will be provided with official badges issued by the QSA. The information will only be used for statistical purposes and its confidentiality is protected by law."