I first used vellum in the Ephemera Storage Journals I made to organize my stickers and other little bits. I made the pockets out of vellum and they worked great! They are super sturdy and transparent, so I can see what is in the pockets. Here's a video if you are interested: DIY Ephemera Storage Journal
I liked the vellum so much, that I spent a week coming up with fun ways to use it in my journals. Here are some of my ideas:
Emboss Vellum
The overlay on the pink belly band on the right is embossed vellum. The vellum looks SO great when it's embossed. I used 112 GSM vellum and it turned a nice white and didn't crack at all (which I worried about).
Don't worry if you don't have an expensive embossing machine. I just bought an embossing folder and put the vellum inside of it and pressed it with a rolling pin. It worked great! I show how to do it in this video: Junk Journaling With Vellum Video
Here's a close up. Pretty awesome.
Heat Emboss Vellum
I have heard a lot of people say that vellum is hard to heat emboss, but I have never had any problems. I warm my heat gun up and keep it moving and it has always worked like a champ.
I topped this paper bag pocket with a vellum strip that I stamped with watermark ink and dusted with silver metallic embossing powder. It looks amazing in real life.
Here's how t looks on the page.
Print on Vellum
I have had great success printing on vellum. I have used 112 GSM and 93 GSM vellum and they both go through my inkjet printer fine. Depending on the weather, there can be some long drying times. So don't print a bunch of vellum pages at once and let them sit on top of each other.
The picture above is a vellum pocket, which has a gorgeous, rich look and feel.
Another way to use printed vellum is in a collage. It blends in so nicely. This is one of my favorite quotes from Mary Oliver's poem "The Summer Day" printed on vellum.
And here it is in a Rolodex card collage.
Stamp on Vellum
I used dye ink (fast drying ink) to stamp on vellum. Then I colored it in with alcohol markers. They looked SO GOOD! 
Then I used it in a Rolodex divider collage.
I've had a ton of fun playing with vellum. Please let me know about any ideas you have. I'd love to try them. jodie@poppiwinkle.com