I was recently asked to give the movie mode a go on a job I was doing. It was essentially just a 360 degree sequence. The camera was on a tripod and slowly moved round in a complete circle. The result was impressive, 1.42min at a resolution of 1920x1080. The file size however was 599MB

My 8GB CF card would last no time and the HD drive would soon get full. Even using DVDs to put resulting movies on would not take that many minutes, and blu ray would no doubt have to be considered.
I've not tried the Mac movie prog on it yet, there was really little need on this occasion, but I imagine there will be some way of compressing or reducing the size in some way. Out of interest though I'd be interested to know what sort of filesizes other people get for a 1080p movie sequence
In the past I have stitched 360 degree panoramas to create a Quicktime VR movie sequence, and I've used iPix camera systems which take 2 180 degree images which are stitched in iPix software. However, it seems to me that those days are maybe gone now and the movie mode in modern dSLR's does just as good if not a better job, without all the hassle, and of course it comes with sound and action if you want it.
I'm beginning to warm to the idea

Nowadays I use the crop mode but if the band do two songs together it can still end being a very large file - at my last gig I clocked up 1.49gb when they segued from one song into another. However, that video is over 9 minutes long. I'm not happy with the quality, but they seem to like it.
The other thing I've noticed with movie mode if you've got the 18-55mm or 50mm lens on is that you have to be a lot farther away or you're looking up their nostrils! This isn't always possible if you're in a bar or club so handheld the videos can be a bit on the wobbly side because it's not always possible to set up a tripod when the club is heaving.
I have just put my movie I referred to above into iMovie on my iMac, and exported it at 1280x720, the file has become 134MB. At 640x360 it becomes 20.8MB and at 480x272 its 11MB
So it seems to me that a client wanting a movie sequence for web use only would have no problem with small versions