If you installed a ROM and all of a sudden start getting strange behavior such as reboots or slow 3g connectivity, this can be fixed. Follow AdamZ instructions for installing, it works like a charm.
Also, some people have reported issues after they had their notification ringtone set to a soundfile that was not stock. I had Zedge installed and had a custom ringtone for notifications, this caused my phone to have some issues when plugging in the USB cord to my computer.
When you install a ROM, do a clean 100% install. Wipe everything, clear the phone (after backing up, of course!), and manually reinstall all your apps. It just saves a huge headache later, you might as well do it right the first time. Once you get an overclocked custom ROM up and running, its well worth the hour or two of effort to do it right.
(note : stole the instructions below from Adam. heh.)
--- Advanced Nandroid Backup First! ---
1.) Download Nandroid Backup *.zip
2.) Unzip *.zip File
3.) Place unzipped folder in "nandroid" folder on your SD Card
4.) Reboot into SPRecovery v0.99.2b (Thanks to SirPsychoS!!)
5.) Select "Backup/Restore"
6.) Select "Advanced Nandroid Backup"
7.) Select ALL options for Backup (System, Data, Misc, Cache, Boot, Recovery)
8.) Name your backup whatever you want (This is a backup of your old OS, data, everything.)
9.) Select "Perform Backup"...
10.) Return to the main SPRecovery Screen
11.) Make sure your computer is connected to your phone and you have ADB installed (skip if upgrading from previous version)
12.) In your command prompt in your SDK Tools directory... type the following commands... (skip if upgrading from previous version)
C:\sdk\tools> adb shell
# format DATA:
# format CACHE:
# format SYSTEM:
13.) Select "Advanced Nandroid Restore"
14.) Select "Choose Backup" and select the one you downloaded.
15.) Choose ONLY "System" and "Boot" to be restored. (I only provided those two, keep your Data. (Only if upgrading from previous version of Wi-Fi Tether App below - WIPE DATA.)
16.) Select "Perform Restore"...
17.) Wait for SPRecovery to finish... then press your top power button twice to return to the main menu.
18.) Select "Reboot".
19.) Give it a minute or two the first time to boot all the way...