Banking apps - WP's biggest issue.
I had an HD7, traded up to a Lumia 800 which I still have because the form factor is excellent for me.
WP7.x works nicely. I'd like the Skype integration that WP8 will (apparently) get but it's not a dealbreaker.
What is a dealbreaker is my bank's piece of shit mobile website. They pretty much don't bother with it anymore because "you should download our app".
What - your iPhone app? Or the Android app that also won't work?
(To be fair, I bank with Barclays in the UK and by all reports, their Android app doesn't exactly work all that well either).
The single biggest nightmare with my phone (and the ONLY reason I'd consider switching mobile OS) is banking apps.
If MS can crack that nut, they're golden. Until then... I shall continue to be unhappy and have problems in recommending WP.