It really isn't. 50% of what I ship goes overseas, and it's disgustingy simple to use USPS.com and get postage rates.

BTW, what's the cost of a Global Priority Envelope?

Here's the issues I have had with international shipping.  If they're negligible in your case, or you've experienced none of these, more power to you:
•        Cost of shipping can be significant, and you will often find yourself haggling even after you set a price.
•        Language barriers can lead to misunderstandings, and foreign words misunderstood can lead to incorrect addressing.  Both are surmountable but require a bit of vigilance.
•        Insuring small parcels is a pain.  Tracking uninsured parcels is next to impossible.  The likelihood of negative feedback increases.  In fact, the majority of my negatives have come from international buyers, even though they represent only 1/5 of my historical business.
•        Variance between countries and rates makes it quite difficult to create a "flat" shipping fee for all countries, unless you're willing to use Global Priority.  The end result is that each international transaction takes a few more minutes -- which adds up when you have dozens in a week, that's another hour or more.
•        Customers who want to pay for air create little hassle.  Customers who want the cheapest shipping possible can be troublesome, because they may not believe you when you tell them how long it takes for a surface package to arrive.  Customers who want air-quality service at a surface-level price are the most difficult of all.
•        I won't post details, but the likelihood of fraud increases significantly, with more limited recourse in some circumstances.
•        Every once in awhile, you will get someone who pays in an unusable format (such as a foreign-funds money order that will cost you quite a bit to get cashed, or a couple times, even foreign currency), or someone who wishes to use a service (such as wire transfer) that you may not be comfortable with due to security issues -- sometimes for yourself, sometimes for the buyer.
•        Modules sent in Global Priority Envelopes tend to have limited padding and protection, unless you get creative with cardboard backers etc.
•        Security issues throughout the world can create havoc.  Recently, increased security in Canada has caused them to issue a release stating that packages must be addressed in all capitals, to an individual first name-last name, not a user ID or company; this has caused me to have a few packages bumped back in recent weeks (I was only made aware of this after the packages were lost for a few days).  This summer, a bomb threat in Dublin caused a $300 shipment of mine to be held in customs for 4 weeks.  The package arrived searched and partially damaged.  In short, due to circumstances beyond your control, delays, damage, and loss are more common than in same-country shipments.

So why bother with it at all?  In my experience:
•        Most international customers are more courteous, and easier to work with.  The exceptions are few, but a major hassle.
•        The market is moving overseas -- with the weaker dollar and more collectors in foreign countries wanting to fill out their collections, I've seen international business increase to 35% of my total, up from 5% in 1999.
•        International customers are more likely to bid on multiple items at a time.
•        International customers are usually friendlier, and sometimes send you cool thank-yous.  I've got greeting cards from Sri Lanka, 3-D hologram stamps from Bhutan, a few antique German photographs, original art from Kenya, thank-yous written from students of English in Chile, Mongolia, and too many other places to mention, and stamps and bookmarks and memorabilia from over 30 countries.  Which brings me to the last point:
•        Catering to international customers is very rewarding.  It really adds to the experience.  Once a month or so, I get a major exception that makes me want to give up on the whole thing.  But then something else comes along that makes it all worthwhile.
8)

Coming soon to an auction near you, more European bidders ...
:P

Dollar sinks after Greenspan's comments - Business - World business | NBC News