Thanks everyone for your comments. My main consideration for the 645
format was the cost, and portability of the system, as well as getting
a negative that could be enlarged more. I shoot landscapes often, but
do some night work, still life and people. Some of the night shots are
quite long, and therefore I do have some concern for the mirror lock up
problem. Given that I do some long exposures, does this rule out using
the 645N?

Also, I'm watching on ebay for other formats, any
suggestions/arguements for 6X6 vs 6X7/others- if so, suggestions on a
particular camera to keep a look out for?

Thanks again,

Dave