I've got a superflash and it's OK at night, but it's really not going to get anyone's attention during the day.

I use a nightrider minewt headlight on flash mode as a rear strobe and it is very noticable from long distances regardless of light conditions. I run it by itself during the day (unless I'm riding in a group) and in combination with the superflash at night. I've had many people on bikes and cars stop me during the day and ask what it is and where they can get one, it can be seen in daylight from over a mile away and is very noticable within a few hundred yards.

At night, I point it down a bit so it's not flashing directly in people's eyes, but it's still very effective and thows a lot of light behind the bike (sort of like an airplane stobe during taxi). What I like about it at night is that people can still see the light bouncing off the road, guard rail, trees, etc., even if another car is blocking their direct view. The superflash really needs direct line of site, night or day.

As others have mentioned, I also believe bright colors and reflective gear is helpful for riding at night. There are no guarantees, but everything you do improves your odds a little bit. I don't mind looking like a dork if it decreases my chances of getting hit (even slightly).