At the start of this month I upgraded my last Debian Wheezy box to Jessie. I'd held out for ages, as it was my home server and had more on it than my BigV public server or my desktop systems.
There were two pain points in the end:
That's all my boxes, both real and virtual upgraded. I've also rebuilt my better half's desktop with a new motherboard & graphics card, so it's now got a significantly faster CPU and GPU, plus more RAM and a much faster main bus to play with. I even managed to freecycle the old motherboard, so that's a win all round.