on the reading of series

When you're reading a series that's one continuous story arc, do you need the non-final book(s) to have some sort of satisfying conclusion/plot wrap even if the larger arc is still ongoing? How much (if at all) do cliffhangers bug you, or everyone being left in dire circumstances? Talk to me about your pleasures & pet peeves with series.

(Yes, I'm considering a multi-book project.)

ETA: I should probably add some clarification. On one hand, I'm definitely curious for general informational purposes. On the other hand, I'm also asking for a very specific reason: I am hearing through the grapevine that because of the economy publishers are less and less forgiving of long manuscripts (especially from newbies) and that staying around (or under) 100k is becoming more and more of a Good Thing. And as everyone knows, I have trouble writing stuff that's short -- so I'm trying to figure out the dynamic between long single books versus two-book series.

ouch

The Elder Child is a freakin' slob. By which I mean she is absolutely incapable of cleaning up after herself. If she pours a drink, she always ends up slopping some on the counter and just leaving the spill there. She'll eat a yogurt and I'll find the foil lid upside down on my sofa and the yogurt cup on the rug. She just can't seem to wrap her head around picking up after herself, which is especially bad now that I've got two crawlers in the house who like to put things in their mouth. (And no, she really doesn't seem to get the concept "choking hazard" either.)

Anyhow, I was making dinner and decided to put the kettle on for tea when I noticed a fine brown haze of chocolate milk powder all across my stove, and without thinking just went to brush it off with my hand. Forgot I'd just boiled water for corn. Very lovely burn across the palm of my hand, swelling and discoloration and it might be blistering. Also, hurts like an SOB. Already decimated the ends of the aloe plant. Typing is hard. Going to go sulk in front of the TV for the night.