I've had good results with my K-7 for up to 10 minutes in cooler weather (read Canada wintertime), the main issue is that a second frame will be "shot" to determine and remove "hot" (or malfunctioning) pixels. The upshot is that a 10 minute exposure becomes 20minutes. this process (which kicks in after 29 seconds exposure time on the K-7) does make images a bit softer.
Another option if you are working off a tripod (which I assume you are, given 7min exposures), and if your subjects aren't moving, is to exposure stack several shorter exposures, and use photoshop to combine the images and remove the noise. This is common for astrophotography, and works quite well.
I bought a timer remote, which has the added benefit of allowing you to go inside and have a wine and let your camera do it's thing outside, at 2am in the morning or whatever. Also good for timelapses.
The one click open and one click close shutter is very useful if you don't have a release with you. I've used it for night shots If I am travelling with only a couple of primes and an ultrapod while camping, and it has been very useful.
Last edited by Clarkey; 11-04-2010 at 05:21 PM.
Reason: spelling