I was a long time BB user, first a Curve, then a Bold, and then the Torch. It broke my heart, but I eventually made the switch to WP7 because I grew tired of the various "aggravators" that were noticed too often in BB's OS: The hourglass of death, battery pulls, reboot when installing new apps, and lack of 3rd party app support.
Don't get me wrong, I absolutely love my WP7, but there are times where I miss my Blackberry. From what I've seen of the new QNX based OS, BB seems to be making vast improvements. But I feel this might be too little too late (they recently lost their spot in US marketshare to Windows Phone). If I were given a BB10 device, I'd definitely give her a test drive. However, I cannot see myself risking my upgrade on one.... I'll be upgrading to WP8.