Shouldn't have happened with a Vista HCx, if you used logging to the SD card correctly (for any Vista HCx users: log track to the card, enable "wrap when full" so it keeps logging when the internal memory gets full, ignore the contents of the internal memory getting overwritten - it'll all be safe on the card as a GPX file for every 24 hour period).
The 30 isn't quite as bulletproof. Setting it to archive daily seems to be the closest functional equivalent. I don't like it. You have to pay attention to not accidentally delete things when you reset the trip counter. Unlike the Vista's working memory the internal storage on the 30 is huge, and acts as a USB storage device with a FAT32 filesystem on it, so logging to the card doesn't really gain you anything (unless you've crammed it absolutely full of maps, I suppose).