As you know, in the early days of RSS, feeds were restricted to 15 items maximum. In RSS 2.0 that restriction was removed: You can have unlimited items in a feed.
But that doesn't mean it's a good idea to put unlimited items into an RSS feed. Keep in mind that your readers are using RSS to handle information flow. If they start up their RSS reader in the morning and see "Nate's Hamster Feed: 2 new items, Suzie's Menu of the Day feed: 3 new items, Steve's Woodcraft Feed: 1,869 new items," which one do you think is in danger of being dropped?
While it's true that some RSS readers let people filter the news by displaying only RSS items with specific keywords in their titles, who wants to deal with a feed that gives you 1,869 new items each day? The best practice is to limit the items in your feed each day to a manageable number.