Never use condoms with spermicidal lubricant containing nonoxynol-9 for anal sex (unless the other option is no condom at all). Only use them for vaginal sex if you know for certain that you & your partner have a low chance of contracting HIV or other STIs, and you need the extra contraceptive protection. Otherwise, you should use a non-spermicidal condom.
Clearly, any condom is better than none. If the choice is between using a spermicidal condom or using none, the spermicidal condom will be safer for you than none at all. However, if you have a choice between a spermicidal or a non-spermicidal condom, go for the non-spermicidal, and use another form of contraception if you are having vaginal sex and one of you is a woman of child-bearing age. (See below for tips on birth control without nonoxynol-9 irritation).
It was once believed that nonoxynol-9, the common spermicide used in condoms, was also useful for reducing the possibility of HIV transmission. However, nonoxynol-9 has only been proven to kill HIV in vitro (in a test tube). In vivo (in living people), the effects are indecisive. It is definitely an irritant, and in sensitive people, it is believed to actually increase the likelihood of HIV transmission! The following report from the US organisation Planned Parenthood is quite comprehensive and gives references to original research, including the current World Health Organisation guidelines: http://www.plannedparenthood.org/library/birthcontrol/020926_non9.html
Please do link to this post in your own journals, as it is important that people know this. (Linking here would be useful as that way we can keep all the discussion in one place, including further tips from any safer sex educators who happen to be reading this). It's not scaremongering - if you search online you can find many reputable safer sex organisations giving this advice. It appears that the WHO and other bodies updated their information in the autumn of 2002 - if you find organisations still suggesting that you use nonoxynol-9 to kill HIV, check the date on their web site or booklet.
Obviously, most people who use spermicidal condoms for penis-in-vagina sex are wanting to use them as a contraceptive. Condoms without spermicide are only something like 90% effective as birth control, which is usually interpreted to say that 1 in every 10 women who uses nonspermicidal condoms as their only form of contraception will become pregnant. This is clearly non-ideal!
If you are concerned about preventing pregnancy and the woman concerned is able to use a hormonal contraceptive such as the Pill, then you can of course use this as well as a condom - the Pill to prevent pregnancy and the condom to prevent transmission of STIs. However, not all women are able to use other contraceptives. If you or your partner is a woman of child-bearing age and for whatever reason barrier methods are the only method of contraception being used, and the only spermicide available in your country is nonoxynol-9 (as it is for the UK), there are two ways of increasing the effectiveness of the condom as birth control. Firstly, you can put a small blob of contraceptive gel inside the condom to add the contraceptive protection of nonoxynol-9 without irritating the vaginal lining of the woman involved. It has to be a small blob, because otherwise the condom can slide right off! Alternatively (or additionally), the woman can use a diaphragm as well as the condom. You should never use two condoms together, as the additional friction makes them more likely to fail, but you can use a condom and a diaphragm together, because the two barriers are installed at different angles.
I really hope this is clear. I've reworded it about 5 times and added extra information, so the advice is obvious to everyone including the inexperienced. If you still have any questions, then see the web site link I gave and feel free to ask them in comments.