No, I've never seen one before, so I don't have much interest.. They obviously aren't that big elsewhere in the world.
They aren't big you say?
1. Fans and Tuning
http://www.opeltreffen-oschersleben.de/
68.000 visitors (it is for Opel only, no Chevys Lacs or any other GM subbrand)
in comparision:
http://www.woertherseetreffen.at/
180.000 visitors BUT (it includes the whole VAG family Audi,VW,Seat,Skoda...)
2. sales (I'll take german statistics here)
'11 '10 Manuf. '11 '10 change in %
1 1 VW 686 772 613 808 11,9
2 3 BMW, Mini 297 439 266 729 11,5
3 2 Mercedes 285 651 281 240 1,6
4 4 Opel 254 605 233 498 9,0
5 5 Audi 250 708 226 872 10,5
6 6 Ford 230 939 198 156 16,5
7 7 Renault, 160 366 153 555 4,4
8 8 Skoda 142 611 132 150 7,9
9 12 Hyundai 86 866 74 287 16,9
10 10 Toyota, Lexus 83 204 78 708 5,7
source:
http://www.kfz-auskunft.de/kfz/pkw_neuzulassungen_hersteller_2011.html
check the link for a better view to the board, site is in german
Note: German consumers in general are pretty biased on Brand images, much more than in other countrys.
But it clearly shows that Opel, although it's far from beeing the biggest global player, it is neither any close to beeing 'small'.