Shame I didn't post... would have liked a laugh at my own expense. (though back then I don't think my predictions were as bad as some in this thread)
You can't really blame people back then though, there are a number of different types of predictors:
The basic rabid fans of a specific console will generally say yes to any question posed like this (Will [console] sell [X] million) unless it is utterly non-sensical (and back in early 2008 this site was mostly Nintendo fans, though it was around that time that the Sony fanbase started increasing)
The basic fans of other consoles will generally say no, and some of the sensible ones will look at some past data and estimate future sales from there... such as assuming the X360 wouldn't do well due to XB
The statistic whores like myself would look at past trends in detail, and work out probable outcomes based on current trending sales. This may generally be a good method to use, but unless you know some of the business practices and intentions of the big companies, it can go horribly wrong.... for example in early 2008 it was still assumed by many that the success of the Wii must have pushed 3rd parties to start making an effort sometime during 2007, and that the games they actually put money and good developers to would start coming in late 2008.
Again looking at myself, I had little interest in the X360 other than watching the numbers climb on VGC.... given past trends where there is generally 1 leading console (that subsequently gets the brunt of 3rd party development efforts) and that others will fall simply due to lack of support, and with no knowledge of how much money and effort MS and Sony would put into pushing their systems.... as such I think back then I was pegging the X360 to finish round about at 50 million (ie 50/50 chance it would pass 50mil)
Finally you have the crazies like Avinashi, John Lucas and Crazzyman himself (who may have had a decent prediction for X360, but he was also predicting thing like PS3 being 7 million ahead of X360 by the end of 2009)