Based on the format that the Twitter API uses, Kellan Elliott-McCrea created a search engine for the first year of Tweets. The first year consists of 20,000,000 Tweets and can be searched by username and query. If a user hadn’t joined Twitter prior to March of 2008, they won’t show in OldTweets.
A query on a sample term will provide a chronological display of the first Tweets:
The format to use when searching is by user is [userid:USERNAME query]. Here’s a look at @ev talking about Twitter (then still called twttr):
This provides a nice look at just how expansive a Twitter archive search could be. Current Twitter search is quite limited historically, and if you were one of the early adopters, give OldTweets a whirl to see what you were doing 5 years ago.