I use this site exclusively.   
I got tired of all the pop ups and ads that all of the other sites have. I also hate going through all of the crap to get to the good stuff that other sites have to offer.

Here, MaxStyle and DA are the ones I hit every day. Of them, I'd say this is the core.

HOMEPAGE for me is , of course,Desktop Sidebar . . .

~ Very closely followed by Wincustomise , MaxStyles ,Winmodify ~

I have issues with DA ... so , after I got blasted by a coupla' Trojans a while back , I don't bother .... also (present company accepted) it always appears to be full of bucketmouths and bad attitudes .. and rip merchants (must be getting old ...   )

Here of course. I make the rounds to various sites looking for wallpapers about once a month and that's it. Everything I need is right here.

I visit Wincustomize several times every day. I check out Skinbase sometimes and DA sometimes. For the most up to date info and highest quality products nothing I've found beats WC. Last but not least, the people here are the finest the net has to offer.

It'd be interestign to see this "poll" on some of the other sites.
Asking here has a built in bias. 

Good way to get on the turtles bad side.

WC
DA
Skinartistry

I spend a lot of time on tutorial sites for photoshop and recently looking at scripting.

Wincustomize daily easiest/quickest to navigate.
Aqua-soft.org daily which is a forum and more emulation oriented
Deviantart daily but, it's becoming a big time waster.
Hollywoodgui daily

Occasionally:
MaxStyles
Skinnalicious
Customize.org
Skinnables



And I thought it was just me!

WinCustomize
DeviantArt
Skinbase
Winmodify

Almost exclusively WinCustomize but I like the widescreen wallpapers on Interfacelift so I visit there occasionaly too.
I wish WinCustomize would add a sub-gallery for w.s. walls.  

I do occasionally miss the days of Customize.org,Razorart,desktopmod,skinz.org,Sonique.net,etc. Those were the some of the founding sites that really helped launch desktop customization, From which came names still hold a special place among the customization community, Dangeruss,Thredz,Doodle,Lonerunnr,Floach,Wreklesseric,to name a few.


Skinz.org, Customize.org and Razorart were my main pages, til upheavals ensued and the sites either died or became places I didn't want to frequent.

Wincustomize has grown to become the main staple of the desktop customization community, and my home page for skinning. The first site since LiteStep (or SimpleStep as it was called back then) that I actually felt compelled to become an active member.

Deviantart,I use for finding off site stuff.

Artists home sites like Boxxis,Pixtudio, etc.for releases not upped here.

LS.net just for old times sake...

I also go to the apps main page for the occasional skin not upped here. Example: winamp.com

There is also a few sites I frequent just to say hi to pals and offer some support.
Skinartisty,Shaunna's Selections,etc..

MaxStyles
Skinning.net
Deviantart
Skinartisty
CrystalXP (was the first i found)
Skinbase

i visit them once or twice a month. If not everyday i'm here