Great compromise in size, gadgetry, image quality & cost.

I got my Optio S two-and-a-half months ago and I'm extremely satisfied with it so far.
Previous cameras of mine include the Fujifilm Finepix 40i as well as older Fujifilm models (e.g. MX-700).

Criteria
There are about just as many different digital camera types out there as there are different user types and applications out there. For me, the most important criteria was convenience, meaning size and weight. I wanted a camera I could take with me all of the time without bothering me. Image quality was important, but secondary. If you can identify with these criteria, the Optio S might just be made for you.

In the first place, I was very sceptical, when I found out about the rubber laps, the tiny 5-way navigational button, the shutter button, the light aluminium body and the battery life. But after having a second look and comparing it to competitors, I found these not to be an issue. In retrospect, I'm very happy with the Optio's build quality and intuitive operation & button layout.

Competitors
I was considering other models as well, including the Casio Exilim Z-3 as well as the Exilim S-3, and furthermore the Canon Digital Ixus II and 400 (a.k.a. Canon Powershot SD100 and 400)

Optio vs. Exilim
Although I liked the larger screen on the Casios, the Optio has just as many pixels. When taking a picture, one therefore holds the Optio more naturally closer to the head rather than holding it at arm's length, like the Exilims. Also, the Optio doesn't require you to lug around a bulky docking station, it comes with a small battery charger and USB cable.
The Z-3 in my opinion is just that little bit heavier and larger, making it uncomfortable to taking it with you at all times. The S-3 on the other hand, was considerably thinner than the Z-3, however, it was taller and wider. Holding all three in my hands, I found that the Optio, even though slightly thicker than the S-3, was the smallest, lightest, most convenient and most easily slipped into my pocket. Furthermore, I haven't regret spending a little bit more for my Optio over the S-3 for zoom and auto-focus.

Optio vs. Canon
I really like the Canon models, since Canon has always been setting the standards for digital compact cameras in terms of image quality and build quality. But when I compared them to the Optio, they just seemed so much bigger and heavier. Granted, the 400's higher resolution is neat, but that also puts it in a different league pricewise. The Ixus II (SD100) has a higher-resolution video feature, but only 2x optical zoom. In the end, the smaller and lighter camera won.

Optio Experience
I've taken several hundreds of photos with my Optio over the past few months and haven't had any problems. I'm very satisfied with the image quality. The flash is great for a camera of this size. Videos are also good. True, battery life could be longer, but it lasts about 150 photos, which is enough for a long day.
Talking to experts, I knew digital cameras are very sensitive. I had to be careful not to drop the camera, or else it would break. When I was at the Oktoberfest in Munich last week, a friend of mine got tangled up in the strap and hurled it onto the (wooden) floor rather hard. However, the camera's perfectly fine, much more robust than I'd originally thought.
I love the neck strap, I always wear my Optio in my shirt pocket, hanging around my neck. People keep asking me if I had my ID card on the strap in my pocket, or one of those new cell phones or mp3 players. Also, I love surprising my friends with my Optio hidden in altoids cans or showing them better uses for cigarette boxes (I'm a passionate non-smoker myself).

To sum it up:
The Optio S is a great camera, when you're looking for a small, gadgety camera to take with you always. There's a couple of flaws, but trust me: When you're holding your Optio in your hands, you'll forget about any flaws and be totally satisfied with you camera!

I bought mine at www.electricsam.com for a great price.

Go to www.dpreview.com and www.steves-digicams.com for great professional reviews.