Chances are that sales will go on well into next year and it'll sell a ton.
I'm not at all worried.
Not least because I know Sonic Colours didn't get to some places on release day... I picked it up 2 days after release because the stormy weather stopped the supply ships from coming into the islands.
I imagine games like black ops are overshadowing the release too.
But if it turns out the game DOESNT sell well then you SOULD be damn 'sad'. If what is easily the best 3D Sonic game ever made bombs then I'd hate to see what kind of message that sends to Sega.
While it's too early to say if it's going to be successful or not, first day numbers are generally a pretty big indication of how the game will perform. Unless there were very widespread shortages of the game, then it doesn't look good at this stage.
Having said that, I'm willing to keep an open mind with regards to the sales, Wii games definitely aren't as front-loaded as PS360 games.
One thing to bear in mind about continual sales though, many of those will be the result of markdowns/bundles/scans etc, and the funding for markdowns comes from Sega's back pocket, not retailers (in most cases) so even if it does sell well down the track, that usually means it's at Sega's expense.