Actually, I've had pretty good luck in my experiences both at Sam Ash in NY and Guitar Center here, w/ the exception of one time in the Pro Audio dept at Sam Ash when my usual sales guy wasn't there. 

Worst is, I was shopping for some serious gear and that's one one time where they could have influenced my decision, but I walked away after asking them 2 or 3 questions and didn't buy a thing. I guess they did influence my decision. :) 
 
Beepster - yeah, that's probably what I do. The least I have to go out, the better. And my wife and I are both Amazon-aholics.

I haven't tried the Cobalts yet, but I think I have a pack in my storage.  I did try Elixirs when they first came out..quite a while back.  They felt great and sounded good, but seemed to go dead very quickly.  And when THEY went dead, they were DEAD.

My mainstay for years and years has been D'Addario XLs  9-42....but I do occasionally use the heavier bottomed 9- 46s.

Ya... it's a good thing I don't have any money because I'd blow it all at Amazon and NewEgg... not to mention all my new money soaking friends in the music software world. DARN YOU TO HECK, CAKEWALK!!! 

As far as music stores they always treated me like I was going to rob the freaking place... until I picked up an axe and started playing. Then they'd be tripping over their danglies to get at me. Jokes on them though because I didn't have money back then either. I was usually just there to pick up some picks and strings. LULZ!!!

The electrics are pretty easy to keep up with. You can buy those in bulk and get a good deal, always keep new strings on. The acoustic? I play with the nano-webs, and they're a bit more... But still I definitely replace strings when I record. The 12 string hurts a bit more.

But the bass players among us? We really take it in the shorts... However, and again? Having just put a fresh set of rotosounds on the fretted bass for a project I'm working on? Life is too short to play w/dead oxidized strings... And it F's with your intonation. 

Seems Amazon and D'Addarrio come to the rescue of bass players as well.

http://www.amazon.com/s/r...-keywords=bass+strings

I'm lol'ing at the "used" set being sold for $45 though. Wat?!

Rotosound baby... (for the fretted) 

And I do play the D'Addario warm mellow flat wound on the fretless. But I know many different strings are good? What's more important is the instrument, then it needs to be set-up with the strings you are playing, and the strings need to be fresh... After that all of the other "stuff." pre-amps, plugs, performance, etc... The list is long, but it starts with? A piece of steel and nickel "vibrating..." It all starts there, so that part is very important. 

Life is too short to play w/dead oxidized strings. Don't clean them, "replace them." 

There used to be a brand called No Fame and back when I actually played bass in a couple bands they saved my freaking life. Everything else was at least $35. A pack of No Fame's was under $15 and they were pretty darned good. I haven't been able to find them for years though. I just used my last pack of them on my P-Bass. They had been hidden in all my crap for god knows how long. Glad I found them though. I had neglected to invest in bass strings and needed to track some stuff. They are gonna have to last me a while too.

Yeah, it's stupid when you think about it? It's just raw materials, and a winder? I've seen how they make um. And they can crank them out en-masse? So I guess the rest is just marking, the hotties in the booth at NAM, the steak dinners for the sales reps, etc. I do like the Rotosounds though...

Starise

 
 What should I do when not playing a guitar for awhile? Should I be: loosening the strings slightly to reduce stress on the necks? 

Nobody has touched on this, but I don't believe you want to do that.
Even though the strings may lose their tone, they balance the tension of the truss rod.
I periodically tune the strings of unplayed guitars to maintain the tension.
I'm not sure how scientific it is, but most of my guitars are over thirty years old, and the necks are still straight.

I think it can depend on the factors as mentioned above. I play the Ernie Ball Skinny top, heavy bottoms 10-52's. I play rather hard & we practice twice a week and gig 3-5 times a month. I generally change the strings on my main guitar no more than every 2 weeks. For me, it is to avoid breaking them on stage. I tend to break the low E, & A strings. My other guitarist plays elixer strings (I think they are called) and has to change them because of rust due to the acid from his skin which is weird cause his guitar looks pretty nice. the hardware(especially the bridge) on mine is so rusted it looks like a relic off of the titanic!