One big strength of internet forums is the access it gives newcomers to the field to many people with vastly more experience, and the oportunity to ask them for advice.  With the exception of the odd letter that is answered, this is not something you can do with a magazine.  If you buy one magazine you get reviews of the few items in that issue, with possibly some sort of very brief summary of recent reviews near the back; you do not straight off get access to all the knowledge of the reviewers, stretching back over a number of years.  For the more budget conscious, magazines also of course have the understandable floor that they in general only discuss new purchases, whilst internet fora can give good advice on what is available 2nd hand as well.     

Magazines can have advantages too of course.  Magazine reviewers get the chance to listen to a wide range of equipment, for extended periods of time, without the pressure of having to choose to buy it or not.  For those of us outside the trade this simply is not possible.  For some fora posters there is always going to be the tendency to defend/promote equipment that you've chosen to buy, although I guess magazine reviewers may have the same trouble with their kit in their own systems. 

It of course goes without saying that HiFi forums are great for the social aspect  .

Martin