It's important to note that wind power in Denmark only works at that scale because they can export it to Norway and Sweden. Those neighbors can absorb variable power output while load balancing their grid with hydroelectric dams.
Hydroelectric is currently the only economical "grid-scale battery", and it is not available everywhere.
Yes it is up to date. The info/about section is a great read -- he talks about the reason he created this site, the source of the data and also explains the software stack: http://www.gridwatch.templar.co.uk/about.html
Is it actually up to date and accurate?
I wonder if wind player a major role somewhere where they really have a lot of turbines. Like Netherlands or Germany perhaps.
Would be really interesting to be able to compare different countries with the same sort of data.