Google Chrome - Flash on Youtube issue
Solution 1:
Honestly, I think that's just part of Flash on OS X. You could test the same YouTube videos in other browsers, as Chrome contains its own Flash rather than use the /Library plug-in version, but every YT video I've played on a Mac has always had that buffering pause a few seconds into it. (Vimeo is usually smooth.)
There have been some sorta-hacks to set Mac browsers to use HTML5 instead of Flash, however: you might start with Jon Gruber's always-excellent blog though that may be somewhat outdated.
Solution 2:
You should try click 2 flash, a free extension for safari that puts a grey box in place of flash elements which aren't run until you left click them. The great part is that it detects youtube videos are runs them in a native video viewer (i'd say quicktime, but i'm not sure, might just be html 5) that's super smooth.