is this important?

Given the enormity of the Sichuan tragedy, and the tiny number of potentially thwarted out-of-the-closet lesbian Chinese blood donors - no, it's not a big practical problem. It's rather marginal.
But it is important symbolically because it brings up just one of many inequities in the Chinese system. The mere act of an individual being able to criticize a patriotic state function -- collecting blood for victims -- is important. You might not think everyone's opinion is significant, but at least they have the right to express it.
There is also wider discrimination here. In a document outlining who would or would not be allowed into China during the Olympics period, Beijing singled out many groups, lumping rowdy protesters along with those with sexually transmitted disease and mental illness. Of course, most of the world would consider it discriminatory to bar HIV-positive people from coming to your country just to visit, and it seems like China has learned little from the kindness of people like Dr. Gao Yaojie. Also, barring the mentally disabled seems ironic given that China has made such a deal out of the Paraolympics. They may use the imagery of brave athletes in wheelchairs (who are indeed admirable), but I don't think Beijing really understands that people who are different, or who have unattractive problems, must also be treated differently.
If China wanted to screen for cleaner blood, it should bar men who frequent brothels, not women who chose to be with other women.
And, no, I don't think the US Red Cross is right on this one, either. But the whole U.S. approach to AIDS -- the whole context there -- is different.

This is a recurring challenge in any public health intervention: balancing individual rights and the common good.

Any group statistics confronted to individual disparities would eventually be considered a failure if you try to make it fit everybody and every situation. And this is not the point of those statistical tool. Rather, they use trends found in larger groups to support decision-making.

It's a question of minimizing risk for the larger group even though it may mean discriminating another at some point. Of course, who, why and when you discriminate has to be continually reassessed (scientifically, but also socially, politically and economically) in order to reach some balance.

Blood donation issues are touchy. Past cases of blood contamination has affected thousands of peoples'lives and costed governements millions.

I guess the question is: would allowing everybody to donate blood without considering the "HIV statistic associated with their race, ethnicity, class, religion, sexual orientation, nationality, or gender" significantly increase the risk of contaminated blood transfusion?

Would the social benefits of non-discrimination outweigh the potentially increased risk?

My guess is yes, but I wouldn't know for sure. Epidemiologists?

As for lesbians in China, if they are indeed at a lesser risk of contracting HIV-AIDS, it is a mistake to consider them a "high-risk group" and prohibiting them for donating blood.

Speaking of Dr. Gao -- If China wanted to identify high-risk activities, it should look back at those poor Henan farmers who donated blood and contracted the disease innocently and unknowingly through state-run blood collection programs in the early 90s. Of course, the state is more careful about these things now. But that case of dirty needles, lack of education, plus greedy & corrupt officials, offers lessons to be learned.
Probably the top spreader of HIV in China is prostitution, particularly the type that is mixed up with high levels of trafficking -- meaning that the women don't have as much choice to use condoms as they may like. If Chinese officials wanted to "crack down", they could start in just about any hotel lobby or bar!

However lesbians are only excluded because forms listing groups prohibited from donating blood use the term “同性恋” (tongxinglian)

Which includes you, the willing lesbian donor, only if you say it does.

Or does China put 同性恋 on ID cards now?

I understand the discrimination issue, which should, naturally, be deplored. But it's hard to see this "policy" as any hindrance whatsoever to any wonderful lesbian person who wanted to donate blood, for Sichuan, or any other reason.

On the larger issue, of disallowing "high-risk" groups from donating, that makes perfect sense in the context of an imperfect testing regime (ie. the one in China, exacerbated by a natural disaster).

If all blood was tested all the time and all tests were 100% accurate, then of course there would be no need for any such policy. Sadly, all blood is not tested all the time, nor are the tests in question anywhere near 100% accurate.

I've never understood why they even ban gay men from donating. There is nothing stopping someone from saying they aren't gay just so they can donate blood - the regulation relies entirely on the honesty of the donor. HIV might be more prevalent on a per capita basis in gay men but it is not just a gay disease - in any case, all donations are screened for HIV. I would have thought that given Red Cross is always looking for blood that wouldn't want to turn away any potential donors. Maybe there is some other reason I don't know about. Can anyone explain the rationale?

I work at a blood service and every unit that is drawn is tested.