I think very well of the UNAIDS site -- it is the closest thing the planet has to a "gathering place" for AIDS professionals. The UNAIDS team did a good job with the relaunch last year (to see from where they've come, here is the UNAIDS site in 1997 -- minus a few graphics.) I hope they continue to push the site, though:

First, while it dominates in the AIDS space, its metrics still are not dominant compared to other major policy-oriented sites. Here is a list of "links in" by Google:

UNAIDS: 11k
UNDP: 16k
UNICEF: 18k
UNEP: 24k
US Dept. of Ed: 28k
US EPA: 93k

Second, I suspect that folks at UNAIDS still view the Web as one of their secondary efforts, when in my opinion it should be the principal focus of their efforts. They have a huge comparative advantage, a good head start, and should think very ambitiously about the features and resources they add online in coming months.