It's a feature where notifications will light up if you pull the phone out of your pocket, or wave your hand over the phone without depressing the power button (peek mode). There are settings to have it constantly on. I have mine set on my wireless charger where Glance is on continuously. At night, I can take a quick "glance" at the phone while it's charging and see what notifications I have. I like the email notifications of WP8.1 because I can set it so that I can tell how many in each of my different email accounts I have, rather than the sum of all messages.
Wow. That sounds really awesome. I shall have a play with that tomorrow when I get it 
Are there a load of customisation options?
You can customize a reasonable amount. Instead of icons, there are tiles, similar to widgets. They be arranged however you like on your start screen. It's easy to put custom ringtones on WP8.1. Wallpapers/lock screen are pretty easy, just like Android.
I have heard a little about the home screen customisation, but I was just wondering specifically about the glance feature. 
With the Glance feature, you can set how long it's on when you activate it. You can set it to "Off" (Glance deactivated), "Peek" (Glance turns off after 30 seconds), "Interval" (Glance turns off after 15 minutes), or "Always On" (self explanatory).
When active, you have four content settings to choose from: Date, Detailed Status Notification, Quick Status Notification (each of which can be set to "On" or "Off"), and Background Photo (lets you choose just a black background with white text or a color background).
It also has a Night Mode Exception feature that lets you change the text color to red, green, or blue, or it can also just deactivate the glance screen entirely. As hinted, it's good for night time viewing so you don't accidentally blind yourself with white light from the text. Also, there is an "Off" setting which leaves the Glance screen as is.
It's a feature where notifications will light up if you pull the phone out of your pocket, or wave your hand over the phone without depressing the power button (peek mode). There are settings to have it constantly on. I have mine set on my wireless charger where Glance is on continuously. At night, I can take a quick "glance" at the phone while it's charging and see what notifications I have. I like the email notifications of WP8.1 because I can set it so that I can tell how many in each of my different email accounts I have, rather than the sum of all messages.
Wow. That sounds really awesome. I shall have a play with that tomorrow when I get it Are there a load of customisation options?
You can customize a reasonable amount. Instead of icons, there are tiles, similar to widgets. They be arranged however you like on your start screen. It's easy to put custom ringtones on WP8.1. Wallpapers/lock screen are pretty easy, just like Android.
Additionally, the tiles can be set to two or three sizes (depending on the app associated with the tile... most do all three sizes, but certain ones like Amazon or Newegg only do two). Also, you can set the tiles to a range of colors or have them be transparent and show a wallpaper behind them. I actually posted a screenshot of my start screen here on GH. I'll have to see if I can find it for you, katushkin.
EDIT: Here we go...
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Thanks for a some more explanation :) That looks awesome, I can't wait to mess around with it :p
Well, have fun with it! Go buck wild!
