On Friday, Liz (Googler) at the YouTube support forum posted a thread at the YouTube Help forums about why some videos get stuck at the 300 view mark.

Liz explained that when some videos become popular very fast, YouTube takes longer to figure out if those views are legit or not. So it can take several hours for YouTube to update the view counts to reflect the accurate views. Let me quote Liz:

The issue is that many YouTubers are noticing their view counts getting stuck at 300 for a lot longer than just several hours. Some are complaining about them being stuck for several days, if not weeks. I am not sure what the issue is there or if it is a spam issue or not.

Forum discussion at YouTube Help.