been out sick, here are some grouped replies
I am not sure that 'cart' laptop are necessarily more work than desktops. 
And I would never question the #s that Tommy has rolled on costs (Tom, just 
support costs or total everything costs?) but here are some thoughts ...

They to tend to be slower, and locked up (slow to get to) but they also tend 
to be used less. I think there is a correlation between volume of use and 
failure (software or hardware) so, given that laptops are used less, I have 
seen that they break down less, and otherwise have less maintenance. I have 
also on occasion been able to take a laptop with me to work on (on another 
project, home, into a meeting) not so easy with a 50# tower. The laptops are 
generally also treated better, and have better supervision, so kids try and 
destroy them less.

I can fit a laptop cart in my office, I can then work on all 16 of them in that 
space. Having them all in proximity saves time with maintenance. I would not 
try to stuff 16 desktops in here!

Another way I have saved time it to drag the laptops to a standalone lab. 
While the standalones are rebooting or scanning, etc. Boot up the laptops. 
Helps soak up some of that idle time.

We have gateways that are 5 years old, some HPs that are 4 and 3. Each of 
them still get 95% of their original battery life.

Battery on my 1 year old bottom of the line dell laptop is maybe 66% of 
original runtime.

Extended warranties are useless unless you need them. Catch 22, so we skip 
them and hope to avoid the lemons.

We have had 2 laptops dropped from waist height and survive 100%. No other 
known/reported issues here ...

>lifespan vs. flexibility
laptops are by their nature compromised machines and will not last as long as 
a same cost desktop. Slower proc. less RAM to start with.

Some of our teachers LOVE taking their laptops home, others leave them 
chained to their desk, batteries out for months at a time  ... 

I love our wireless printer ...

200 computers 400 students 80 faculty k-12, k6 sixteen laptop cart, 7-12 
fourteen laptop cart.

1 FTE me, official title is tech & integration support. 30% of my time is 
earmarked for integration. I do servers, desktops, firewall, filtering, email 
virus/spam, buyer, hoarder/disposer of junk, dealer of ink. Heavy on the doing-
more-with-less lately and a choking dose of find a cheaper solution ... 

Hope all are well.