Twitter is a victim of it's own success with millions of users now and a staggering number of tweets per week.
The current message ID is 3685068820
A week ago an id was 3514807126
That's an increase of 170261694
In software development, ID's like this are stored as an unsigned (positive) long which in general has a limit of 4,294,967,295
So (4,294,967,295 -(3,685,068,820 - 3,514,807,126))/170,261,694 gives an end date of the last week in September THIS year, 3.5 weeks from now.
They should give a prize for the person whose tweet is the 4, 294,967,295th
Then again maybe they are using a different range. Mysql, which rumor has it twitter used initially (bad idea), has a bigint range of
-9223372036854775807 to + 922337203685477580.
This would give them, at the current rate of growth,
5.41717387 × 10^9 weeks . That's a 5 with 9 zeros .
This would last them until around the time our sun expands and destroys life as we know it.
Who'll tweet that.