Yes! Intonation on the guitar is a huge problem - much bigger than people realize. Because of this, only a few players with amazing pitch/vibrato control can actually play a good sounding and slow melody with sustained notes.
Also, many chord voicings will sound horrible without some kind of modulation effect (ie chorus) to hide the out-of-tune notes.
After a while we learn to work around this problem, some people even argue it's not a problem and that it just adds character to the instrument. But I think the guitar is so sensitive to our input that we don't really need this kind of additional handicap.
Yeah, I don't think it's a 'problem' at all. It
can be annoying on a crappy instrument or one that is horribly out of adjustment.
We've been tuning
more or less to what we now call 12-tone equal temperament (12 tet) for a long time (JS Bach, 17th cent). Pianos, keyboards, all fretted insts and most keyed/valved wind and brass insts are pretty 'fixed' as far as their intonation is concerned. It'll only even become an issue when a fixed, equal temperament instrument plays in an ensemble with 'justly' tuned instruments. And even then I bet most folks wouldn't even notice the pitch discrepancies.
A well made guitar or bass with a proper set up as well as a player that knows how to properly fret a string not to mention tune their instrument can play very in tune, long melodies as well as thousands of different chord voicings in all keys.
Equal temperament was an incredibly liberating discovery allowing large ensembles of varied and different instruments to be able to play together in tune and in more than one or two keys. In fact 'equally' in tune (or equally
out of tune if you're a baroque era cynic) over all 12 keys. It made modulation possible. The importance of equal temperament to western music can not be over stated.