I called up my local Ultimate Electronics to see if they had the Image X10s in stock.  Turns out they don't right now but I need a new set of headphones soon.  (I found out Ultimate Electronics is a Klipsch authorized seller and I can buy a 2 year warranty after the Klipsch one is up with UE for just $25).  My first question is: how long can you wear the Custom 3's before they start to feel uncomfortable?  Also, since I am by no means an audiophile, do you think I could decifer a gigantic difference in sound between the Image X10s and the C3s?  And my final question is: is it really hard getting a good seal with the C3s, because that's kind of detering me from getting them over the X10s.  Right now I'm leaning towards the X10s but am strongly considering the C3s.

gigantic difference?  I have no idea.  I've never heard the X10's but own the C3's

How long might you wear them before they start to feel uncomfortable?  Dont' know there either...  If you have them well fitted, I'd expect you could go a long day with them feeling just fine.  I've had mine on for probably 6 hours...  (doubt much longer) and will admit, my ear feels a bit of relief when I take them out.  When I do that, I'm usually on the tractor or my backhoe and have over ear protection on as well.  My ears always feel better when I take those off too so are they adding to my issue?

No idea.  The extra silence (from machine noise) the C3's give me as well as the addition of music in my head is well worth any discomfort.

My specific issue with them is when my ear sweats, they will rotate a bit as I turn, strain or do other weird things with my head.  I can clench my jaw and realign them so they are always coming into and out of sound with my ear.  I get the most useful sound of them when I use the standard (large) tips.  I tried the double flanged tips and found when they got out of alignment, they STAYED out of alignment and I had to fiddle with them with my hands and couldn't clench my jaw to realign them.

Don't know if that makes sense and regardless of how negative it MIGHT sound (not sure it does, this is a 'just in case' comment) I gotta say that ALL of these tradeoffs are VERY worth it to me for what they bring me with enjoyment.

I specifically chose the C3 style because I knew I'd be out & active with them and I wanted the ear wire.

 Thanks for the info on them 

Also, I was wondering if it took you a while to get a good seal with them the first time you got them

I tend to wear my C3's on a for 15 hours or less.  I might get a little irritation in the ear canal if I take them in and out often to talk.  What I do instead is turn my volume down or unplug the cable to minimize the chaffing. 

As far as fit.  If you don't get a seal for proper bass performance you may need to bend the wire so the eartip points up and or forward a little more.  This is what I had to do the first time.  Once it is adusted it usually fits right as long as I keep them in the case to protect the bend on the wire.  It takes some people a month or more before they "get it".  So a little patience may pay off.

Good luck!