Hi Cruisindub,
Personally, I wouldn't use a blade. You can score the glass and then when you re-tint, it looks terrible.
Heat is your friend. A heat gun is your best bet. I've done it with a hairdryer before, but you've got to have a stonkin' hairdryer and it's a bit more work. I've not got a steam gun, but have used a spray bottle to mist water on while using the heat gun before, and that does seem to work well. Basic heat guns are pretty cheap these days (plus it's a good excuse to buy a new toy). Just be careful if it's cold where you are, and you wack a heat gun straight onto the cold glass...
If you're having trouble grabbing the film to peel, consider using a credit card or plastic paint scraper. Go gentle (you want to get under the film and lift it, not scrape at it from above), and it's less likely to do damage than a sharp blade.
For car windows, you can take them out and submerge them in a hot bath of dishwashing detergent - works a treat. Not so good for house windows though.
Once you've got the tint off, you can clean up any left over glue residue with WD40. Try it on the section you've already done. Spray it on, let it soak, then hit it with an old rag. Don't be afraid to add more WD40 as you go. Fantastic stuff.
Apologies if this is too basic.
Good luck!
Matto
