Decided to stick with a Windows based phone when upgrading from a Palm Treo Pro 850 running Windows Mobile 6.1, after consideringing some of the iPhone and Android options and getting feedback from friends. The OS is designed for integration with a Windows Live (Hotmail) account as would be expected from a Microsoft OS.
Overall I am very happy with the Optimus 7. Applications run quickly, the device is easy to handle and just about fits in a jacket pocket. Battery life is just over a day when using email, a few phone calls and some browsing; basically it will need to be charged every night, which seems typical for most of the recent devices in this category. Expect not much more than 6-7 hours if listening to music and using WiFi.
I use the phone to pick up 2 MS Exchange email accounts, a Hotmail account, and a Gmail account. All work well and the Calendar integrates all of these into a single view which is a big plus for me.
The device is not flawless, the camera button on the lower right is easily pressed by accident, however the pictures taken are quite crisp from the 5 MegaPixel camera. Being ablse to take photos without unlocking the phone is another advantage. Windows Phone 7 does not come with a native Messenger so you need to go to Marketplace to get the available IM applications, I have used Messenger by Miyowa which isn't the best. I have also used Flory for Google chat which works ok. It also requires installation of Zune software on an associated desktop/laptop to synch music and other files, so cannot exist on its own.
Pros: Good email integration, lots of available Apps on Marketplace, solid device. Fast browser. Photos taken can be automatically uploaded to a Windows Live account, which is handy for real-time backup. Answering calls and taking photos can be done without unlocking the device.
Cons: Battery life could be better, available IM apps aren't great (probably improve over time no doubt), location of camera button.