My Desktop Client is also depending on since_id right now in order to display the user all new tweets since he logged out. Also without since_id and max_id it's not really possible to implemente a "more" link at the bottom.
Personally, for my needs it would be enough if since_id and max_id would be replaced with since_date and max_date, as that wouldn't affect my application since I'm not relying on the tweet ids but only need to retrieve tweets in a specific timespan. But one thing for sure, there needs to be a replacement. To unsubscribe from this group, send email to twitter-development-talk+unsubscribegooglegroups.com or reply to this email with the words "REMOVE ME" as the subject.
