Is there any practical effect of reversing solid and stripe, when wiring cat5 cables? But if I've got a cable where each pair is a pair but one end is flipped, will this make any practical difference for 100BASE-TX? For 1000BASE-T? For POE (power-over-ethernet)?
As long as it's reversed on BOTH ends then I can't imagine it would matter at all. Of course, if someone one-day re-terminates one end correctly then you're likely to have issues.
Depending on which pair it is (you didn't mention), for 100BASE there's a 50% chance that it won't matter since only 2 pairs are used; 1+2 (Orange) and 3+6 (Green).
For the sake of an extra 2 minutes and a 20 cent plug, cut it and do it right would be my advice.
if the reverse is on both ends then there is no problem.
for 100BASE and less, reversing pair polarity on one end will probably not work. however, I have seen chipsets that are tolerant of these wiring errors. I think this has become more common since the introduction of Gigabit Ethernet.
for 1000BASE and 10 gig, pair polarity doesn't matter. some chipsets are even tolerant of swapped pairs. this is becoming more common because it costs almost nothing to implement.
so depending on your hardware, the practical effects could be minimal.
To add to what's been said for data, it won't matter at all for POE since the voltage is applied across the pairs, not within them (1-2 and 3-6 for Alternative A, 3-4 and 7-8 for Alternative B).