Great thread.
Personally, I like an exaggerated bass for HT, but a tight and accurate bass for music. It's a bit tough to find a good blend rather quickly.
I use to have my crossover set at about 65 Hz or so, but recently I used the cut-off frequency built in to my receiver (90Hz) and set my Studio's to "small". This has really helped me get a better blend with my main speakers in most ranges. The only downside to this is that my old receiver's cut-off is fixed at 90 Hz....once in a while the sub gives itself away. I'll gladly accept this rare and small annoyance for the improvement I got. Not sure exactly at what frequency bass signals become non-directional, but I suspect around 80-85 Hz. When I finally get my new receiver with better bass management I suspect this will be taken care of.
I always thought the "small" speaker settings were for those little cube HTIB speakers, but boy was I wrong. Not only is the bass more accurate now, but the mid and high frequencies seem to be handled better by my speakers now that low bass isn't a concern for them. My Studio 40's are about 3 feet from the back wall, and 2 feet from the sides, toed-in with some curtains and small shelves to act as acoustic treatment. The sub is about a foot away from my front left speaker in between it and the TV, and a foot out from the wall.

As for SPL calibration...I fool around with my speaker level setting every week...I can usually be off by anywhere between +7 and +3 dB's. I cannot do what an SPL meter does by myself, even though I swear they sound right to me. After I calibrate it with the SPL, adding 3 dB's sounds a bit louder. A system won't sound bad, but it does sound better when it's calibrated with an SPL meter. Personally, I think SPL meter's are the best $40-$50 dollar investment you can make in your system...just think, everytime you bump a speaker, move it an inch or two, rearrange furniture, etc, it's there for you. Helps allow for some really cool side by side amp or speaker comparisons too by ensuring the volume is pretty much standard between the models your comparing. Takes some of the bias out.
You can usually get one cheap on ebay.