Also, I find that I really don't like this game of upgrade... It ids a losing proposition. Buy at x, sell at x-y to buy z which is also experiencing depreciation... It is a losing game... losses everywhere... It is rough.
I think my problem that I buy used like new gear all the time... So I don't lose money on my lenses... But on my bodies... It is nerve racking.
Camera bodies always depreciate, though, and the longer you wait the more they depreciate. But how much do you lose? I recently sold my 5DIII for c. $300 less than I paid for it, which means that for the 18 months I owned it I paid $16.66 per month. Seems like a pretty good deal to me even though I do photography for fun and didn't get paid anything at all to use it.
I do that math all the time... but generally what happens is I will buy a used like new lens for $800, use it for a year, then sell it for $900... so my cost of ownership is -8 bucks a moth.
I broke even on my xs. Over two years of ownership I lost $320 on my 60D... and that still breaks my heart (13.33 per month). And now with my mkiii, I paid $2500 (us warranty), and if I sold it today, I'm looking at maybe $2100 back... so $400 over 24 months give or take... so 16-17 bucks per month... and that's fine... but that's today.
In 6 months the mkiv comes out... let's say @ 4000, so if I sold the mkiv today, I would still be looking at 1900 for the ugprade... if I waited a year, I would be looking at $1000 upgrade and about 2 years without a full frame body.
It really is something I have mulled over... but there is no way that I'm going to use my daughter's t4i for 2 years or even 8 months...
So I'm getting out of the upgrade game... I'm going to use my mkiii for about 4 years... 5 if the mkv is delayed, and I'll probably be looking at $4500 ($3500 for grey market 1 year after launch) and maybe $1300 in resale value for the mkiii (If I'm lucky), so still $2000 for an upgrade.
So after 6 years of total ownership... I'm still looking at $16-17 dollar per month in depreciation... so it is just exhausting.