Whenever I'm poisoned, by a spider or whatever, I can find no ill efects to my character. There's nothing negative in active effects. Am I looking in the wrong place?

Yea.... not much reason for Cure Poison potions or racial preference.

Honestly most poisons used by creatures like spiders or falmer fall off so damn quickly that unless you open your Active Effects part of the Magic menu the second you see the message, its effect will probably have already worn off.

Unless of course you're a vampire or werewolf in which case you don't have to worry about those things at all.

Pretty much what Gallarialchiban said. The only time I've been quick enough to the Active Effects menu to see anything was when poisoned by Chauruses and even then that was at lower levels.

There are 2 types of poisons. One is regular poison and that's one time effect, so you wouldn't notice it in active effects. Then there are lingering poisons, which does damage over time. I noticed that some of the trap poison darts are lingering damage types. And Frost Spiders have lingering 3 second damage poison attacks. If you are attacked by a poison it's most noticeable in 3rd person view. You change color (green?) a bit and your health goes down for a bit.

Why are they so weak as to be nearly inconsequencial? I seem to remember in Oblivion poisons lasted longer.

Abacus707 has it right. Things like the Chaurus and Frostbite spiders blur the vision for a bit, but it isn't a debilitating effect over time. Or rather, damage over time (dot). The arrow traps do have a lingering effect, as I've seen my health go down ever so slightly faster than it regenerates.

OTOH, I don't bother with frostbite venom on arrows when I'm going to one-shot the thingy anyway, or it's some resistant thingy, like draugrs.

Im not 100% sure but I think that if you get poisoned enough times within a certain amount of time you contract a random disease.

Try to clear Falmer dungeons at lower levels and you won't think poison has negligible effect. It knocks down your health pretty significantly.

Hmm, I'm lvl 58 and the Falmer Shadowmasters can give me a run for the money.