what world are you talking about?!!
I think I have seen much more gambits of sound and unsound nature on chess.com rather than in tournament play. the only gambits I have witnessed in OTB are the King's and Queen's gambits. not a single Danish! how weird...
At my club I see the French Defense played against me (with terrible success :P) on a regular basis. Online I rarely see any mainline french lines.
At the club I also see the Grunfeld a lot, I rarely see it online.
Oh and the scotch is WAY more popular at the club than online.
Edit - TOTALLY forgot about that damned pirc! I face it all the time in OTB, never online, and I hate it! I score super well against it but it bothers me to no end that people continue to play it!
My theory: Simpler lines that require minimal memorization tend to be the favourite of the older folk that can be found at a chess club. Online, people are more comfortable having a battle of opening theory because databases are a click away.
I haven't noticed much difference really. Maybe people online for some reason tend to lean slightly more towards e4 and OTB d4, just very slightly..
oh! the four knights and the scotch gambit always pop up in the clubs and tournaments. while online the four knights defense is a big "no!" and the scotch is rarely seen.
online I see many players adopt a Pirc... and then train it to be a Lion or a Hippo, thankfully at the local club not many people like to risk themselves seen playing a weird and possibly dumb opening.
Which openings have a vastly different popularity on the net compared to OTB? For example in about 100 games as white I have never had someone play the Grunfeld against me. Also I had never seen the Svesh in play before using this site.