Gmail - How good is the spam filter?

I have been using my Gmail account for close to 2 years now and for the first time today, I happen to have a "false positive" in my Gmail account. A legitimate mail from my trekking acquaintance was tagged as "Spam" and shoved into "Spam" folder.

I am quite impressed by Google's spam filter tool. For more than 700 days I have been using Gmail, it has done its job to perfection of filtering mails which contain profound How-to guides to expand or shrink size of private parts of body, highly educative information like how to get cheap credit or how to get software without paying for it, day today general knowledge oriented info like the latest price of Viagra, Valium, Cialis etc. man it sounds as though life would seriously be dull without these.

now this incident triggered a thought as to how other spam filters perform as against Gmail. Luckily Danny Sullivan of Daggle has done all the hard work and have compared the spam fighting capability of 3 spam filter services Yahoo, Gmail and Spamcop and compiled this report.

The report looks interesting..Yahoo with 5% false match percentage..hmm..thats not very good when compared to Google's impressive 0% and spamcop's 0.2%. Also the number of spam messages caught by Gmail and spamcop is lot more than that of Yahoo. Probably one metric that I believe would be nice to have in the report would be "number of mails which were spam but were not tagged as spam by the spam filter". Can we get that metric from the data given? I guess no. If someone can..I admit now itself, I am bad when it comes to logic and math :)

As a parting thought, if I write, say Viagra - $10 in Mspaint and save it as image and then add this image to body of the mail, is the spam filter technologically advanced enough to read the image and tag it as spam? Something similar to what Riya does with photos. Probably will try when I will have lots of time to kill.