About Taiwan specifically, it depends. Sometimes upgrades are cheaper, sometimes not (depending on the manufacturer and the type of item you’re getting). The store also makes a big difference: Any store that looks halfway decent (by US standards) will almost always have high, near-or-at-retail prices. A lot of the computer stores there have merged into big electronic shopping malls over the past few years, increasing both their appearance and prices. Gentrification, I guess.
Is your girlfriend still there? You could have her check prices for you before you go.
Basically, the more generic something is, the bigger the difference you’ll see (compared to here). RAM is somewhat cheaper, cables are dirt cheap (none of that $30 Belkin crap), and software can often be cheaper. Compared to China, however, Taiwan is still relatively expensive.
On the other hand, non-generic things are often more expensive. Name-brand graphics cards (i.e. ATI and Nvidia-based) are about the same or more expensive, even though they’re often made there.
As for iPods, last I checked they were significantly more expensive there than in the US. Being an Apple product, the prices don’t seem to fluctuate all that much and you have to pay sales tax unless you can find a shady tax-dodging store – but that’s not entirely too difficult. You’ll also likely end up with Chinese documentation and software, if that matters to you. Add in the currency conversion rates and I dunno if you’ll be able to find a good deal there.
On the other hand, crappy generic MP3 players are a dime a dozen there.
And about your GF’s experience… that’s probably because France is more expensive, not because Taiwan is cheap. It’s not illegal to put pictures and documents on your iPod (at least not the latest ones). They’re intentionally designed to be usable as portable hard drives (you just click a checkbox in iTunes).
FYI, stores there usually don’t have return policies so you have be careful about your purchases. It’s also likely that the manufacturer warranties won’t carry over to the US.