Did this accidentally, of course. It would seem to be an unwise thing to do.
Is it?
I leave mine on stand-by all the time. Sometimes for days.
I dunno, I leave my desktop on hibernate all the time, but it is plugged into a surge suppressor. Isn’t it bad for any computer to be plugged in, even if the power’s off, unless it’s got a surge suppressor?
I also leave mine on standby most of the time. I’ve seen no real harm from it. I do try to turn it off now and then 'cause rebooting clears caches and stuff like that (or something).
The only hazard with standby and laptops is if you leave it that way and also not plugged in. Standby draws some power, though not as much as normal operations.
So after a couple of days of battery-powered standby the battery will eventually discharge & you’ll be left with an uncontrolled shutdown of Windows. Which can harm Windows by leaving trashed data on the disk. Not highly likely, since entering standby mode includes flushing all data to disk, but the possibiillty is still there.
I should have said my laptop was plugged in - as it is 98% of the time.
But how about the laptop’s hackability when left on standby? Is it increased?
I leave my laptop on standby all the time (and plugged in). The network card shuts off when I close the case. Is there a light that indicates if your network card or plug is on or off?
People (like me) leave their desktops running, not on standby, 24/7 and and it’s no more “hackable” when it’s being used than when it’s not, provided you have the right firewall and AV settings…
unless you have a recent mac laptop, they enter a ‘deep sleep’ before the battery drains which cleanly writes a disk image out.
http://www.macsimumnews.com/index.php/archive/macosg_sleep_vs_deep_sleep_mode
Only in the event of a damaging power spike (which in most locations are tolerably rare).
I leave my PCs on 24/7
Only if you have something like “wake on lan” turned on. Someone probes the laptop address, the laptop wakes up, it is then completely on and can be hijacked like “normal”. But since the same attacks work when you have the laptop on for real, not a huge increase in danger.
You’re worrying too much.
Thank you for allaying my fears. 
Vista has a similar Hybrid Sleep mode.
The only problem I’ve run into was closing my laptop during a mapping program while a GPS was hooked up. It went into the blue screen of death when I opened it 10 minutes later. You’d think after getting it rebooted that I would learn not to repeat the process. Had a hell of a time getting the data off it the 2nd time around. Took a friend of mine 7 hours to fix it.
My work laptop stays on for days or occasionally weeks at a time.
Cycling the temperature of parts inside of PCs is hard on them, and there is a debate about whether leaving them on or turning them off daily is better for this part or that part.
Leaving my desktop connected to a GPS NMEA talker has caused trouble in the past. When I return to it, I sometimes see the mouse pointer shooting all over the screen and clicking on things, and a deep mat of dialog boxes and windows all over the screen - I think the PC sometimes gets confused and treats data coming in from the GPS as mouse movements and clicks.
Nine times out of ten, when I think I’m leaving my laptop on standby, I’m not. For some reason it hates going on standby when I close the lid. And if for some reason it DOES go to standby, the slightest jiggle or touch of the case will pop it out of standby.
So if my computer’s fine being on ‘not really standby’ almost constantly, I think you’re ok 
I’ve gotten into the habit of just closing the lid on mine when I’m done, that way it wakes up automatically when I open it back up.
My laptop (Win XP) on stand-by still plugged in will remain in stand-by until I wake it; if it’s on stand-by and on battery after about 15-20 minutes it hibernates itself. There are settings you can manage regarding how it’s supposed to behave, although mine ignores these settings.