Conveniently, the first IPPC report in 1990 focused on a 110-year time frame ending in 2100. Less conveniently, subsequent reports have each decided to emphasize a shorter time frame than the one before it, because each one also emphasized the 2100 time frame. If the Fifth AR due out in 2013-2014 time frame does the same thing, then people now alive will be in their 80's and still have their remaining lives relegated to a far-off time bin.
Choosing a maximum human life span is a good boundary zone for long term analysis. What that life span would be needs somewhat arbitrary delineation. The link above shows there are hundreds of people now alive who reach 110, so that seems pretty safe as a minimum number for a reasonable, maximum life span even under current, primitive technology, and again it matches what we started with in 1990. It would also have the advantage of reversing the increasing tendency of recent reports to downplay climate impacts by emphasizing shorter time periods.
The Fourth Assessment did look at conditions after 2100, but not in great detail and grouped together with impacts heading out to 2300. The Fifth Report will also look at impacts after 2100, in an as-yet unclear fashion. It should change the categories to say, up to 2125 and then after 2125 (UPDATE: corrected my problems with the advanced mathematics of addition). If not, then at least should provide much more detail as to what could happen in the early 22d Century, because it's appropriate to consider what current generations are going to face.