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:
Recently we have seen questions about why some YouTube video view counts "freeze" around 300 views. To help prevent confusion, we wanted to post a quick explanation of what's going on. View counts are extremely important to our community, so we work hard to ensure those view counts are accurate. Occasionally, when a video becomes popular quickly, it takes our computers longer to make sure those views are accurate. This means a video's viewcount may not update for several hours, sometimes allowing ratings and comments on the same video to climb temporarily higher than the views. So if you see your video views aren't moving, or that your video's comments and ratings are moving faster than your views, don't worry. If you're still getting views, the count should update soon.
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.