I'll just keep this updated with secrets I find on the website after decompiling it...

Code:
preorderBtn1 = new preorderBtn();
This would seem to suggest that there will be some sort of retail release. This is also supported by the button in the top right of the page that has a hidden method of purchasing the game (Xbox LIVE, PSN, WiiWare, ???). I don't know about you, but I've never pre-ordered a downloadable title.

Code:
broniksBtn = new Sprite();
Not sure what a "Bronik" is. Speculate away...
Also supported by this XML line:

Code:
<broniks text="BADNIKS" />


These images (placed together for this screenshot) are found within the decompiled website materials. It could suggest a blue character (Sonic), green character (Vector? Jet?), yellow character (Tails), and a red character (knuckles). These images are currently unused (AFAIK). This could also suggest the methods of purchasing the title. This seems like the more obvious answer to me, blue being WiiWare, green being XBL Arcade, red being PSN, and yellow being the final form of download. Any guesses as to what yellow is? EDIT: Yellow appears to be the iPod Touch. Interesting...

Code:
zone1Btn
zone2Btn
zone3Btn
zone4Btn
zonesBtn
There are only mentions of zone buttons for 1-4. To me, this code suggests the first episode will only include 4 zones to play your way through.


There will also be a music player on the homepage coming soon The above is a mock-up image using the buttons from the decompiled website. All of those buttons will be used in combination and will look very similar to the mock-up. Their test song was something from Buddy Holly. True statement.

Code:
<track title="Buddy Holly" url="../assets/music/track1.mp3" />


Just a hidden promo image. There are a few of these, but none that really interest me.

EDIT:
Definitely worth mentioning. Ohai, Mike!