Do "camera bags" actually work? Recommend compact waterproof camera?

I'm an amateur with a Canon 520HS and a 50D. I'm going scuba in a few weeks and have considered the compact "tough" camera:

Nikon AW 110Olympus TG2Panasonic TS3/TS4

But none of them seem to be reliably waterproof to 10m ( from the reviews I've read).

So I'm re-considering a housing for either my 520HS or 50D. Do "bags" like the "DicaPac" actually work for my casual purposes of 10m snorkel and scuba?

Thanks for your input...!

bags are very useful to protect your gear above water. I use them when im in the beach (for phones). The problem with bags underwater would be pressure, even if it stays dry, the bag will be pressing on most, if not all, the camera buttons due. YMMV

Bags are good splash protectors!

Period.

Sealife cameras are reliably waterproof point and shoot cameras.

If you intend to stay at 10m scuba and snorkeling, there are high-end bags that are quite secure. I just tried out the Ewa Marine with my D90 a few weeks ago and it felt perfectly safe. I used it for pool shots and some shallow water diving.

There's a model where you can actually fit your regular strobe inside, so you get a DSLR setup with lighting for a few hundred dollars. It's not like having a real underwater housing but for that price it's well worth it. The buttons are kinda hard to reach, especially the command dials, but if you set it above water you should be fine.

I wrote a full review about it if you're interested: http://blog.housingcamera.com/underwater-photography/ewa-marine-u-axp-flexible-underwater-housing-review

I might use a bag at the surface but wouldn't venture to any depth

no matter what the manufacturer told me.

http://www.ikelite.com/web_two/can_elph520.html

I'd go for a "snorkeling" camera, as mentioned, above.

The issue with bags is getting all of the air out of them, so they aren't so buoyant. While the volume decreases, due to water pressure, they are still a big of a handful.

You can also find used Canon housings and bodies (like the G-9) for not much money (around $400-500). Might check the classifieds here.