Very strange! Can you upload a .zip of your composition so we can take a look?
Edit: I also checked out your composition in Canary (the beta channel of Chrome) and didn't see an issue, so the problems you're seeing look like they should be fixed with the next stable release of Chrome.
Thanks for taking a look, I have uploaded it here but removed the sound to make it smaller file size http://www.chaplinmultimedia.co.uk/client/egreeting.zip
The version I have is Version 23.0.1271.64 m on Chrome
I am working on something using the same snow effect and had the same issue. I found what is the cause of the jittery animation. What I did to fix this was open up the jquery.snow file and comment or delete out the -10 from the endPositionTop = documentHeight and the same with the - 10 + Math.random() * 200 in endPositionLeft = startPositionLeft. This makes the snow fall straight. Also lowering the number of snowflakes helps alot too. I hope this helped!
Thanks for your suggestions it reduced it a bit but it still moved quite a bit in Chrome. It is strange why it is affected seeing that it is rock solid in the other latest browsers.