Is it just me?

Tony, didn't mean to suggest that my post was the only possible interpretation of the OP. But, I know exactly the kind of experiences you relate to. In fact I think we all do...enough so that I imagined Mlman probably understood that as well and, likely as not, was originally prompted to post b/c he was wondering if there was some sort of technical reason for what he was experiencing within the context of his own system...of course, I could be wrong on my presumption...Mlman??

Point taken. My system can give me goosebumps now and then which I think is related to quality of reproduction but the emotional connection is all about the musician, I think.

Another overlooked factor is the quality of your system's electric supply. Generally speaking, a system will sound better during low grid demand hours (late evenings) and worse during high grid demand hours ( daytime weekdays).
High temperatures can also decrease a system's sonic performance due to the extra demands on the grid from home and business air conditioning usage. All of the home and business electrical equipment connected to your neighborhood's electrical grid and any noise this equipment introduces, between the power generating plant and your home, does nothing but degrades the quality, and can even fluctuate the quantity, of the electricity supplied to your audio/video equipment.

I notice my system sounds best later in the evening when the weather is temperate. This is not meant to discount the other factors already mentioned thus far.

Tim

It would appear that weather plays a large role, with wet conditions and low pressure systems being quite bad for the sound, the electrical grid most likely being affected. It would also appear early mornings and nighttime are better times for critical listening. It's difficult to prove other than by tracking sun spot activity over at the National Weather Service site, but sun spot activity might influence the sound, I wouldn't be surprised. Not to mention the myriad things we change in the system without paying much attention. What ever happened to keeping a log of changes we make, even seemingly innocuous changes, like arrangements of cabling, absolute level for the turntable or CD transport, etc.?