Is a subwoofer 'overkill?'

i just bought a subwoofer hereabouts. The deal want well and i hooked it up. i can certainly 'hear' it. My wife is agast.

Yes, even at the lowest settings it sounds a bit loud.

Thoughts. Should I save it for movies? Turn it off when she gets home?

Note; This is a woman who can hear changes I make when I roll my tubes, better than I can. She know even when I don't tell her.

Bummer: the wife has zero appreciation of high-end audio, but hears better than me.
Sounds like it's not set up properly. Possible that:

1) the crossover point is set too high so that it is doubling up frequencies already output at good volumes from your main speakers
2) the volume is still set too loud
3) the placement is bad

I recently added two subs and found that an SPL meter helped a fair bit to verify what I was hearing. I don't have true flat response but I have been able to get it close enough that my system definitely sounds richer without the bass playing any louder than the rest of the music.

Bottom line - keep experimenting - this takes days, not hours...
Sounds to me like there isn't optimal integration. When crossovers, phase & level are correctly adjusted, there should be no distinct impression of bass heaviness or low frequency accentuation, just a sense of greater acoustic space, a clearer acoustic window into the music that's fleshed out with harmonic completeness. A good start for inexpensive help is Rives Audio's calibrated test cd that's designed to work with the Radio Shack SPL meter. It really helps to use a bit of calibration dialing these things in. Level, contour, phase controls, etc. don't always have effects that meet logical expectations.
Pull the sub further away from the room boundaries to tame the loudness factor, or sell the wife... :^(
Assuming you're running a powered sub, connected with RCA's.

I'd suggest using Rothwell 10db attenuators, which will allow you adjust the pot on the sub to a much more optimal setting.

I use this method with my Sunfire sub and it allows for a MUCH smoother intergration with my main speakers.

It really makes a HUGE difference.
You may be exciting room resonances that were not evident before. If the SW does not have its own equalization circuitry try a Behringer DEQ2496. The RS meter and Rives CD will set you back about $100. For $350 or less the Behringer will do a better and much easier job of showing you what your problem is, and after that it will fix the problems, which the RS meter will not do.
Velodyne SMS-1 EQ/RTA is the way to go. You can smooth out the bass peaks/valleys and when the wife gets home, put it in night mode in which reduces output up to(user adjustable) 20%-90%!
+1 on room mode excitation. Try some different locations away from corners and walls. Set your crossover on a low setting and then bring your output level up until you can detect the sub working. Women are more sensitive to low frequency then men.
Download the test tones from the M&K pro web site and verify the level calibration with an SPL meter.
My main speakers are good to 25 hz, so I only use the subwoofer when me and my boys want to watch some testosterone driven, explosion filled movie and rattle the windows. My wife usually goes shopping during this time. :)
A well set up subwoofer is seamless and doesn't draw attention to itself. In fact, you should have guests asking if it's turned on. The biggest mistake most people make is turning up the volume too far on a sub. A little...a very little...goes a long way...yet it will still be a significant addition to the system's sound.