Some vWallpapers for the iPhone can cause Winterboard to lock up or otherwise become unusable.
For this (and other) reasons, set BossPrefs as your double-tap-home application! You can do this from the "More" section of BossPrefs.
If you have this issue, and SSH enabled, you're still in luck. Removing the offending packages will restore your iPhone to working order. Cydia is simply a graphical front end for the APT tools: if you know the name of the package you need to remove, simply ssh in as
root* and run:
apt-get remove <package name>
However, the package name is different from the friendly package name. Here's a few examples:
com.touchrev.dramaticchipmunk - Dramatic Chipmunk
com.stephen.surprisetheme - Surprise
com.touchrev.afroninja - Afro Ninja
To recap, you can remove Dramatic Chipmunk via SSH by executing:
apt-get remove com.touchrev.dramaticchipmunk
What if the application you're trying to remove isn't listed here? To discover package names by searching descriptions, try:
apt-cache search <keyword>
Searching for Surprise might look like this:
localhost:~ root# apt-cache search surprise
com.stephen.surprisetheme - A theme showing off some of WinterBoard's powerful new features. The result is both stunning and beautiful.
*Installing and removing packages can only be done as root.