[Update 1:09pm. Correction and further points below, in italics.]
Earlier, Ben took the position that it’s best not to get too worked up about ridership numbers at this stage, and I think that’s true whether the numbers are good or bad.
That said, Link’s first-week weekday boardings were just announced via press release as 12,000/day. For reference, that’s slightly higher than the ridership of the 7 — Metro’s busiest bus route in the Rainier Valley and third-busiest overall, and one that serves a denser population. Link would be second overall, slightly behind the 48.* Of course Link has much higher capacity — vehicles are more frequent, much larger, and provide a longer span of service — so any individual train is likely to appear quite sparse at that ridership rate.**
There were 16,900 boardings on Saturday the 25th, and 16,100 on Sunday the 26th. This was no doubt boosted by the many events last weekend, as well as first-timers who skipped out on opening weekend for one reason or another.
Sound Transit projects 21,000 daily boardings by the end of the year, as people figure out their commutes, bus service is realigned to better support Link, school starts, and some duplicate bus service is cut. The 2010 figure (once Airport Link is open and the second round of bus changes happens) is 26,600.
There were 1,300 boardings on the airport shuttle bus per day, so about 10% of trips are airport trips.
And before you ask, boarding estimates are based on sensors that perform sample counts of people getting on the train, not on ticket sales and ORCA taps.
* Comparison is skewed somewhat by a lack of Link numbers for when school is in session.
** There are about 248 one-way trips per day, so the mean trip would carry just under 50 passengers, meaning about 1/3 of the seats were full on a 2-car train.