[...] Tendency for the pens to clog when the printer sits idle for several days and how much ink is expended to clear the clogs? I read that the Z2100 doesn't even have a maintenance tank which I guess means no waste... true? I can't tell from the product description, does the Z2100 come with a stand or is that an option?
I do not have any experience with the Canon, so I cannot provide a comparison. But, I do have an HP Z2100 for two weeks now and I am happy with it, even though I bought a used one (with only 31qm printed). Having the Z2100 idle for a while (my experience is days so far) there is no trouble with clogging. Depending on how long the printer might have been down simply carry out a nozzle test and/or small sample print to ensure that your final print will be okay. And, the printer has a self detection system, which will tell you when something might be wrong with your printheads. Even if a printhead maintenance is necessary the ink consumption is pretty low, somewhere around 1ml per ink (provided no head is clogged, then it will be a bit more).
Yes, the Z2100 does not have an ink waste tank, HP is convinced that their system does waste almost no ink! It has two ink sinks instead. They should be inspected time by time to be sure that there is not too much ink in it. The user manual recommends to use a piece of cotton to clean it out if necessary. Since I haven't read anything negative on the ink waste thing anywhere you shouldn't worry about it. Overall it saves a bit of money, since you don't have to buy waste tanks.
And yes, the Z2100 comes with a stand which seems to be well constructed.
One thing that let me stay with HP (upgrading from a B9180), amongst others, is the easy and less expensive printhead system. When the time has come (after years or several square kilometers of printing) a new printhead (for 2 colors each) is only around 55 Euros.
Have look at
http://z3100users.wikispaces.com/ for more detailed information on the Z2100. Though the site is dedicated to its big brother the 3100, most things are also true for the Z2100, since they are of the same technique.
Thomas