This is what my collection of jumbo crochet hooks looks like. 
These hooks range from size N/10mm (at far left) to T/22mm (at far right). The skinny yellow stick horizontally across the center of photo is a size H/5mm for comparison.

Funny to think of an H hook as 'skinny' huh?

Some hooks are much longer because they're Tunisian hooks, but I can use the short hooks for Tunisian crochet too if they don't have thumbrests. 

Jumbo hooks are all-out fabulous for Tunisian crochet. For the Tunisian Mobi-Dickie (top right column) I used a short 10mm hook. Seems like something good happens every time I use a bigger hook than usual with Tunisian stitches. In fact, that's how I got all inspired with the extended Tunisian knit stitch used in the Tunisian Shakti Scarves, and the Neck Lattice (see red photo, lower right column). It has always looked dense in stitch dictionaries, but switch to a jumbo hook and it gets all lacy. Effortlessly.

Jumbo hooks are also all-out fabulous for Slip Stitch crochet. This satisfying 1- or 2-hour 'Collapsi-Cowl' is fresh off of my Q/16mm hook. It's giant slip stitches in giant yarn (Cascade Magnum and Classic Elite Twinkle Soft Chunky). It makes slip stitches more fun than ever. I enjoy this kind of yarn more too. The stitch texture has a fresh look and feel. This experiment pairs two slip stitches for the collapsing accordion effect.

Jumbo hooks sizes are weird. A standard Q hook can be 16mm or 15mm. (Causes problems for new designers, ask me how I know.) The 'standard' sizing of jumbo hooks http://bit.ly/tbaPXh is pretty crazy all around. One size covers a range, while other sizes are simply missing. The jump from a Q/16mm to an S/19mm can interrupt a design, such as this cowl: I also made one with an S hook, and I like things about each; therefore a non-standard "R" hook would be perfect.

Jumbo hooks can turn any common crochet stitch into something uncommonly lacy. This has fascinated me for a long time. For example, the Mermaid Shrug is single crochet in the front loop using a jumbo hook, but several crocheters have questioned whether it's crochet when I've worn it at conferences. (Pub. in Big Hook Crochet ©2007 http://bit.ly/uq15kW ). The other day, Doris mentioned the Curiously Easy Lace Curtains she designed with single crochet and a big hook. http://bit.ly/suSzD0

But, these are summery things to make with jumbo hooks. I'm going to go crochet some more plush, thermal, cozy warmers. I'm eyeing some roving I bought at a fiber fest, even though I don't have a spinning wheel any more.
 
Almost forgot to mention: Alpine Cup Cozy was recently uploaded to Ravelry and is still $1.99 there. I used an L/8mm crochet hook.  http://bit.ly/vpbcGE