Notifications was one of the original motivations for creating SearchYC, but there are a couple of fundamental flaws:

1) How would we know if you've already read a comment/submission? It would get spammy really quick unless we did some kind of periodic digest. We decided that creating RSS feeds for search terms (e.g. username) is a happy medium for this, but we're open to suggestions.

2) New items can take quite a bit of time to get indexed (usually 0-2 hours depending on the number of new items and position in the queue).

That feature should be part of any internet discussion software, but 99% of the time, it isn't. We're still in the stonge-age of discussion.