Twitter just rolled out a new way of handling notifications which I think for the most part is a good thing. Notifications are now sent by default (unless you turn them off which you can do here) for @ replies, retweets and when somebody 'favorites' one of your tweets. Personally I like this functionality but for people/entities with a higher volume of tweets I think this will be an annoyance and one that is likely to be misused. Spammers can now RT or 'favorite' a tweet by a big brand/business/celebrity in order to get their name/URL into said entities inbox in the form of a notification from Twitter. I expect most celebrities and larger corporations will disable this feature but for the average Twitter user I think it's fairly useful.