I'm on an 18 month Dolphin 35.
500 anytime minutes, unlimited texts, unlimited Internet.
First glance at the HTC Desire is making me think that the UI is even better than the one on the Nexus.
Not sure about the hardware buttons yet, but that's probably because I have gotten usd to the weird touch buttons on the Nexus.
As to apps I've been using on the Nexus:
Amazon MP3 store
Ringdroid (allows you to make ringtones/alarms/notifications out of any medial files you have (i.e. MP3's)
Mileage (MPG tracking app)
Network Monitor Pro (keeps track of data usage on both WiFi and 2/3g seperatly, very nice if you don't have an unlimited data connection)
Locale (does things depending on triggers, i.e. when I get home it turns on wifi and turns off bluetooth, when i get to work it turns off wifi and gps, when I plug headphones in it autoplays music)
ConnectBot (Telnet/SSH client)
WiFi Analyzer (scans for AP's and shows what channels they are on, signal strength, will analyse and suggest a better channel to set your wifi up on to avoiid interference from overlapping AP's)
Network Discovery (IP and port scanner)
Dolphin Browser (replacement for default browser)
beebPlayer (like iPlayer, but will allow you to stream over 3g if you aren't on TMobile or 3 [the official one won't])
Race Ace (It's a GPS based lap timer which also logs the g's with the accelerometer, then will plot the results over google maps
Grav-O-Meter (Gravity/acceleration meter [shows your acceleration due to gravity in all 3 axis])
I think it's also about time we had a Android forum like the iPhone one, as I reckon that HTC are going to steal a massive amount of customers with this phone and interface.
edit: Rooting will allow you to run certain apps that you cannot when not rooted, but it does invalidate your warranty, as it also allows you to do things like overclocking it. It also allows you to install custom firmware roms like the Cyanogen Mod where some very clever people have pulled together all the best bits from all the Android implementations on the different platforms and combined them into one. For instance the N1 doesn't allow tethering, by rooting or custom firmware you can enable usb and bluetooth tethering and also WiFi tethering (i.e. the phone becomes an AP for wireless devices)