Just curious what you mean exactly when you say to "open TiBU" after skipping past the google registration?
The few times I've switched ROMs, I've always had to re-download titanium from the market. I haven't taken the time to really familiarize myself with the file-system yet. So, I was never sure where the TiBU apk was stored.
Is navigating and reinstalling it from the SD card the preferred method after a wipe+flash? If so, where do I find Titanium on the file system?