I recently added Video Units to my web page. For some reason, only a very low number o impressions are appearing. For example, I had 250 page impressions for Adsense Content and only 9 page impressions for video units. Is Video Units just slow at reporting the impressions, or is there some other issue?

Are the video units on all the same pages as your regular AdSense units are? Keep in mind that you don't get paid for the video content itself ... you get paid for the graphical banner ads that are built into the player. Are they house ads by any chance? Other than that, it's possible the reporting is just delayed. Did you just put it up within the past 24 hours?

I didn't tried adsense video unit yet. But I think it's the ads unit and link unit that are effective in adsense.

I'm actually surprised how well link units work for me, considering they're so small and require two clicks.