How to Hard reset your phone easily.
YOU SHOULD BACK UP ALL YOUR DATA SINCE THIS WILL ERASE EVERYTHING IN YOUR OS SIDE.
Discard what you read in your htc handbook.
1.)Turn off your phone.
2.)Press and hold Vol. down key
3.)Press and down enter key in the center of your phone (the wheel)
4.)Then power back on.
Voila, it should give you the hard-reset screen. Much easier then pressing on the reset button etc etc.
Be sure to backup everything because this will erase everything in OS side, including contacts.
How to backup your contents.Windows XP *You need to have outlook installed in order to save & transfer your contacts
Use Microsoft activesync provided by sprint in a cd.
If you lost the cd, here's the link from microsoft.
http://www.microsoft.com/windowsmobile/en-us/help/synchronize/activesync45.mspxConnect your phone to your pc and follow the sync setup screen. (Basically pick what you want to sync)
Windows VistaComing soon.
x64 of windows vista do not allow activesync.
How to download all of your folders from your email account.
In your "Inbox" go to Menu -> Tools -> Manage Folders.... Select the folders you want to synchronize.
Courtesy of phelanx
How to your own mp3 as your own ringtone.
1. Place your mp3 in the my document folder.
2. Go to settings
3. Go to Sounds
4. Click on ringtones and select your ringtone. (Usually in the bottom)
How to remove unwanted programs from your phone.
Settings >> System tab >> Remove Programs > and select the program that you no longer want.
How to block ads from Opera Browser. - from XDA forums.
ad-block is a well know feature on browsers, which can avoid downloading contents (e.g. ad) with a set of rules.
Now I discovered the Opera mobile does provide ad-block feature (named content blocker, same as that on desktop)!
To proceed, download the following preference file,
http://adnsto.net/other/urlfilter.iniand paste to your diamond's Windows\Opera9\ directory
An ad blocked example:

How to change themes from your phone.
Start>Settings>Personal>Today then just select which theme you want
or use Diamond TF3D Config
Give me some more time, I'll add more for this tut later.
Also if you would like to add on, please post underneath and I'll put it in the main post.