I realize I haven't updated this in ages, so here's the news for anyone who still cares.
Jan-Michael is coaching Coco Vandeweghe on the WTA tour, after being her WTT teammate for two years. You can follow her on twitter @cocovandey, she occasionally makes comments about 'JM' or posts a photo of him. He is still pondering whether or not to get his own twitter account, I personally don't think he should because I am pretty sure he wouldn't update it much.
He still plays tennis as well, mostly with the Boston Lobsters for the WTT season in July, and at whatever exhibitions and cash tournaments he is invited to and can work into his schedule. He plays the Smash Hits events with Elton John and Billie Jean King every year too because he and EJ are good friends.
As for his tennis, well, the very last of his ATP points came off last October. I saw him that week and told him that his points had just come off, he paused for a minute, then said 'well, I'm okay with that' but he still wouldn't say, yeah, I'm retired. For some reason he just won't say that word to me, I'm not sure why. I think he thinks it will upset me. I'll ask him next time I see him.
If you have any questions, let me know. If I can't answer them, I'll ask him.