[myTouch 4G Android Development] signal15:
I did a lot of reading before I did this to be sure I wouldn't lose anything. Here's the step by step for others, since I was unable to find it all in one place. This is for the MT4G/Glacier, no idea if the process is similar on other phones. You should probably still read, but I couldn't find any of this all in one place:

If you flash, here's what you need:

- Rooted phone (if you need to root, search for the gfree method, it's the easiest)

- ROM Manager from the Market. Get the premium version.

- TitaniumBackup from the Market.

- Sync turned on for your contacts and calendars in your google account.

1. Go into TitaniumBackup, set the option to store the settings on the SDCard. Go into Backup/Restore, hit menu, and run the batch to do a full backup of system and user apps/data.

2. Go into ROM Manager. At the top, click the option to install ClockworkRecovery. Make sure it installs version 3.0.0.5. Then click the option to reboot into recovery mode. In recovery, make a ROM backup of your existing ROM. It will store on the SD card. Reboot back into the OS.

3. Go back into ROM Manager, scroll down to Download ROM's. You should see CM7 Nightlies in there. Download the latest build. It will ask you if you want to also download the GAPPS package, grab that also. When it's done, it will ask you what you want to do... just cancel. Go to reboot in recovery mode.

4. In recovery:

- Wipe/Factory Reset

- Clear cache partition

- Advanced -> clear Dalvik cache

- On main screen, install ZIP from SD

- Navigate to sdcard->clockworkmod->downloads->teamdouche and select the CM7 zip for your phone that was downloaded

- When that is done, install another zip from sd, go into the goo.inside.me directory and install GAPPS zip

- Reboot phone from main menu

5. Enter your gmail creds that you used for your primary account from before

6. Cancel the additional downloads thing when it pops up, this will pop up again later after you enable wireless

7. Go into ROM Manager, Select the Fix Permissions option, reboot (wifi won't work unless you do this)

8. Enable wifi and join to your network

9. Eventually you will get the popup again. Select the stuff that you want installed.

It will pull down all of your apps from the market and install them. If you want to restore user data for the apps, you can go into titanium and click on the app, and restore it with the data. Don't do this until it's done updating from the market. Do NOT restore system level stuff. You will cause problems if you restore system level stuff from 2.2 or earlier on 2.3.x.

You should also install SetCPU from the market, set to start on boot, set conservative mode, and create a screen off profile that limits to 368mhz/conservative. In advanced, leave the defaults, except change the cpu up threshold to 75, and the scaling percent to 11 or 12. Massive battery improvements. You can overclock with this also, mine is only overclocked to around 1100mhz. Some people are running 1800mhz. I heard smartass mode instead of conservative is also good, but haven't tried it.

Keep in mind that if you have an HTC phone with the Sense Framework, you won't have that anymore. So if you liked the Sense dialer (which I did), you can't get it. The stock dialer is functional, but not the best. DialerOne and Dialer2 look the most interesting, but they still aren't as good. If you have CSipSimple installed, remove it. CM7 has SIP built into it, and CSipSimple confuses the phone when trying to make calls. If you liked the Sense clock widget, you can get a replacement, search for Beautiful Widgets on the market. The built in camera app is not Sense either, but does all the same things. The Gallery is awesome, best gallery I've ever seen (stacks that you can pull apart and flip through, very cool).

If GPS doesn't work, download GPS Status from the market and use it to clear the A-GPS data and cache. It's the only app that can do it. It's free.

Also, if you want to go back to your previous ROM, you can flash back with the ROM Manager backup that you made. The only thing is, you'll have to downgrade the clockwork recovery bootloader to 2.5.1.2 first. You can do this by flashing a zip from your SD card. The zip is available somewhere on these forums. I don't have a link, but you can find it by searching a bit. The 3.0.0.5 version cannot flash a Froyo or earlier ROM for some reason. I'm not going back, so I haven't done this.

My TitaniumBackup realized somehow that I installed fresh, and it automatically restored my apps and data. It did NOT on my friend's phone. But, he has the free version and I have the paid one. If it doesn't restore your app settings, you can manually go in and do it. One thing that I've never been able to restore is Good corporate email. It restores, but it won't send or receive. If anyone has ideas on this, post them.

Note that I flashed with build 35, and it's been rock solid. Your mileage may vary. If you already have the software noted above, the whole process only takes about 5-10 mins.

Edit: Recovery 3.0.0.6 was released, and works with 2.2 and 2.3. So you wouldn't have to downgrade the recovery to go back a version. As of this edit, you can grab it here if it's not showing up in ROM Manager yet: http://xdaforums.com/showthread.php?t=952433