I much prefer the WP approach to mailboxes--you can combine different mailboxes as you see fit. While my wife was in school and working I had her email on my phone so I could let her know when anything important came in. I could combine my email accounts in one linked inbox, and her accounts into another linked inbox.
As for apps, in general I haven't had any problems with finding what I need in WP(7, fwiw). But I mostly just browse the web (and like IE9 for that matter), stay in touch with email/text/messaging (integrated FB and MSN, have jiTalk for gchat), have an app for GV texting pinned to start screen with push enabled, the integrated MS Office and Skydrive works like a charm, app for accessing our WHS remotely, weather and Key Ring pinned, multiple shared calendars from different people, and with my ancient Zune Pass (with 10 song credits included) the Bing Music search works awesome in the car.
For that matter...I haven't run into anyone from here in the real world for a comparison like this (which helps my cause

), but anytime I have run into a "we need to look something up" whether maps, info, etc the iOS and Android users are usually still poking around for an app
The voice commands/searches work very well also and leave most people looking rather amazed
Hopefully Verizon gets a nice Lumia with the improved camera at some point.
edit: I think iOS and Android still have a lead for sure in that if you have a specific need for a certain app and it isn't available on WP, that is a dealkiller which is understandable.