From what I've seen so far at work, Microsoft's spam filter is indeed very effective. On my e-mail account, I can't even recall the last time a spam e-mail made it to the inbox. However, it does have the very odd false positive (I estimate 1 in 1000 e-mails.)
I also like how it disables links and images and hides attachments in e-mails filtered, as it means that unless one is expecting the e-mail (to move it to the inbox), the e-mail appears like it is either missing the (infected) attachment or corrupt (broken images and links that don't work), which almost gives away that it's not a genuine e-mail.
It also appears that spammers have turned away from sending zipped executable attachments, as these have pretty much stopped, maybe one a month compared with several a day earlier in the year, probably since most businesses have the mid/large business subscription that blocks such files. Instead, the spammers are sending links that download such files hosted on compromised websites.
One type of spam that does get around this filter is spam sent from hacked Hotmail/Outlook accounts, as obviously Microsoft is less likely to filter e-mail sent from its own system.