Leaving the unit on till the tape/glue accumulates might be a sign that you're leaving it on too long. I like to change the tape/glue while it's still firm and not 'gooey.' It makes it easier to get a clean removal. But mcnash has brought up a good point about the citrus based cleaner. That's another good item to have in your 'tool kit.' I use De-Sovle-It for an extra cleaning tool. You can get it in the home products sections of many stores. I get mine at Wal-Mart.
Regards,
John