A public health blog, which appears to be well-informed.

The U.S. Center for Disease Control information page, including statistics on confirmed cases.  I've not found anything comparable at the WHO site, but please feel free to add links to WHO or to other national health service sites in the comments.

A BBC page with "reader reports" from affected areas–not sure how reliable these are, but some are rather disturbing.   This selection of opinions from UK experts is also informative.

A Slate article offering a plausible hypothesis about why the mortality rate appears so alarmingly high in Mexico, while cases elsewhere are reportedly mild. 

More links to good information sources and reports from readers welcome in the comments.

APRIL 29 UPDATE:  So we've gone in the US from 45 confirmed cases on April 27, to 64 on April 28, to 91 today.  I'm no expert, but that doesn't strike me as an alarming rate of increase, given that now health authorities are testing for swine flu wherever they find symptoms.  The New York cluster may be the most worrisome, since it seems to have spread from those who had travelled in Mexico to some who did not.  My guess, from what I'm reading, is that within a week we'll have a clearer fix on where this is heading.  Warming temperatures in the Northern Hemisphere may help slow the spread, but that may just postpone epidemic or pandemic risk until the fall.  It is possible, as I understand it, that a vaccine could be ready by late fall.

ANOTHER APRIL 29 UPDATE:   There are reports of a suspected swine flu case in a Chicago elementary school child (had to happen sooner or later), but this quote from another one of our gifted public officials in this state caught my attention:  "There's no need to panic at this point," said Dr. Damon Arnold, director of the Illinois Department of Public Health.  I'm glad to know that at some point, Dr. Arnold will advise panic!

APRIL 30:  CDC reports 109 confirmed cases in the US, up from 91 yesterday.

MAY 6:  CDC now reports about 640 cases in the US, though they have loosened up the reporting standards recently, which partly explains the big jump.  640 cases in a country of 300 million obviously isn't particularly significant, though the question is at what rate, and for how long, the case load will continue to increase.

MAY 7:  CDC reports 896 cases in the US.  That's a ten-fold increase in about a week, some of it attributable, again, to more relaxed reporting standards that have resulted in a lot of back-logged cases now being counted.   Will there be 9,000 cases in the U.S. a week from today?  We'll see, though I'm inclined to think not.

MAY 8:  1639 cases "officially" as of today in the US.    That's almost a doubling in one day.  Not good, though perhaps still attributable to confirmation of earlier suspected cases.

MAY 10:  Over 2560 official cases in the US, so no more one-day doubling.  But if it is now doubling every three days, we'll have over 200,000 cases in the US by the end of the month.  If.

MAY 13:  3352 cases, so a doubling over five days, and an increase of only about 30% from three days ago, so a considerable slowing in new cases.   Reports from Mexico of cases of swine flu without fever underline the reality that the total number of cases–as opposed to confirmed ones–is probably 20 to 30 times higher, though the fact that they escape detection probably has much to do with their lack of severity.

MAY 15:  4715 CASES confirmed in the US by the CDC, marking a 40% increase in the last two days.