This is very simple and adaptable to any size of sticky notes or regular notepads, as Kelsey O'Mullane suggested. She uses notepads, the ones with glue on the spine, you can buy packs of 5 for around $2 at the $2 shops. She simply uses double-sided tape to stick them in on the back cover and sticks the refill straight over the back of the first notepad. Eventually you have to remove some pages from the back cover as she says "otherwise you'll end up with a really fat book full of notepad backs..."

You will need
some matt board or straw board (a bit more than twice the size of your notepad)
some glue (I used a glue stick on this project, sometimes I use white glue, I've even used double sided tape or sticky sheets)
some decorative paper
embellishments and/or elastic cord or ribbon

Measure the sticky note pad you want and add about half a cm each way (1/4 inch).
Cut two pieces of matt board of that size. My notepad was 7.6 x 12.7 cm (3 x 5 inches) so my card was cut at 8 1/2 x 14 cm (a bit less than 3 1/2 by about 5 1/2 inches).
Cut a piece of matt board the same height as the matt board covers (if your block of notes is square, you have less to calculate!), and about 1-1.25 cm (1/2 inch) - that's for the height of the notebook. If you want to double up the post it note pads inside the booklet, either by stacking them one on top of the other, or put one in the front cover and one in the back cover, then you should adjust your spine's width. I like making mine at 1.25 cm, but you might prefer yours a bit thinner.

You will end up with three pieces, and your sticky note booklet(s).

You now need papers for the cover, and lining.
Place your two covers, with the spine in the middle (the matt board pieces) and leave a 2mm gap on each side of the spine. (about 3/16th of an inch).
Now your paper should be about 2 to 3 cm larger than that outline (3/4 inch to 1 1/4 inch)- if your paper has a pattern you are specially fond of, make sure it will end up right side up, and that your front cover is aligned in a pleasing manner. Otherwise you end up with upside down designs or cutting off part of a design.

Now you will need a piece of lining paper for the inside of the booklet, to hide the matt board. The lining should be slightly smaller than the outline formed by the matt board.

Using your favourite adhesive (I used a glue stick for this one), apply adhesive on the matt board, and glue it in position on the wrong side of the cover paper.

At this point, you can mitre your corners. I do it a different way: I apply glue in the corner of the mattboard, and fold the corners of the paper onto the matt board, then I fold the sides over, gluing as I go. Make sure to crease your folds for a neater job and to crease around the corner too so that the sides which will fold over, fold nicely and neatly.
I find this way easier as it avoids having corners of the matt board show if you didn't mitre properly... and it looks fine (well, probably not to professional bookmaker, but to me it looks perfect!)

At this point, you can decide to affix a ribbon before covering with the liner paper, ribbon which will be used to tie up the book. I just put my ruler to illustrate what I mean and where you could affix a length of ribbon which would be secured between the matt board and the lining. You would glue the lining on top of, and with, the ribbon.
I prefer to wrap an elastic cord around, usually securing it under the front decoration.

Check the size of your liner, trim if necessary, and glue it to the inside of the post it note book. Take the time to fold the book closed and to score/crease the fold lines so that your book closes nicely. Ensure that you are glueing your liner the right way up so that you don't end up with the inside graphics upside down (yes! I have done that!).

Find a ribbon or elastic cord to wrap around the booklet.

For this booklet I used AM136 XLge Mask Arabian Lge AM143 Med Mask Arabian Sm A blend of Gold, Black, and Red Sculpey III, and a slight application of AUtumn Gold Rub'n Buff. I secured the ribbon behind the large Mask with some E6000 glue.

In the blue sample below, I made a hole on the spine, and put the elastic cord through and secured it with a split pin. The black sample is just a suede lanyard glued with the cast, and tied in a simple knot which is easy to undo and redo.

The two above are for the small sticky pads
(1 1/2 x 2 inches/38 mm x 50 mm approx).

The red booklet below is closed with an elastic cord, held by the glue which is holding the cast on the front of the cover, and the knot is on the left. It looks nice, and is still very easy to undo, and slip back on.

Jeni's sample above doesn't have a closing mechanism, but she cleverly added a pencil holder on the front.

You can use scrapbooking paper to make those books, it doesn't have to be handmade paper, you can also use photocopy paper on which you have stamped or have decorated in your favourite fashion, or even fabric... your imagination will inspire you I'm sure.
Once you've mastered the technique you will love making them and they make great presents for teachers, or to leave by the phone.

You can add tape on the spine if you wish:

or use some contrasting paper after you've assembled the booklet and proceed the same way with the creasing of the gaps in the spine.

 

Hope you enjoyed this tutorial and feel free to ask me (France) questions if you have any. Clever suggestions are accepted too!