issues?  well, i still end up working with various color corrections like levels or blending layers.  i wouldn't call those issues, though.  as i always say, photographers usually adjust the colors on their works.  just clicking render, no matter how much work i do in Poser, can get good results, but nothing i can't improve on. 

if you want to talk about issues though, i'd say

• **anatomy: **i see a lot of errors even i can tell are awful.  and i'm far from an expert.  which, incidentally, makes them that much harder to correct.  i actually need to start studying.
• AO and shadows: sometimes i hit problems just can't be fully resolved in Poser.  that is, i'm getting artifacts of both too high and too low bias.  or i have issues with using both raytraced shadows and depth mapped shadows given a particular lighting situation.
• hair: in any pose but standing there, most polygon hair has problems. i've bought some that move well, but they don't take raytraced shadows well at all.  hair that doesn't cast shadows often creates a bigger problem.  dynamic hair is too resource intensive for results that still need heavy postwork.  and i've never seen dynamic hair that didn't, imho, including some popular posts at CG Society.
• (nudes only) genitals:  sorry, but when i spend ages adjusting the shaders and lights, i really want results that don't look like Barbie.  which puts me in the very, very odd position of having to ask my boyfriend's opinion on how accurate my painting is, much to his amusement. even if it's basically just a line, there's subtleties that make the difference between looking like a painted line and looking like an actual cleft.
• local ambient lighting:  i was looking at a skin reference photo once, and i noticed how  much redder the insides of the woman's arms were. it was surprisingly obvious for something i hadn't noticed previously.  i don't think IBL can account for the ambient effect of the figure's skin and clothes.  i haven't really tried this, because i haven't really noticed the loss, but i plan to soon.
• eyes: i have yet to get realistic eye results, and i very rarely see them.  i have seen someone in the optical profession (i forget what) try to get an eye model to work properly in Poser 6 and fail.  scaling up to 100,000 times helped, but there were still errors with reflection and refraction that prevented it from working properly.  this was obvious when viewed from the side.   another big problem is very visible if you study people's faces on TV even.  or your own in the mirror.  because in real life, shadows don't need a bias, the small concavity of your iris is enough to make it darker where the cornea makes highlights.  i just saw a perfect example of this last night on TV, and though i can't remember on what.  i can say the movie Hard Candy with its extreme close-ups has some perfect references for this.  it isn't visible in mostly ambient or frontal light, but it is in when its very directional.  most eyes in Poser look dead because if they do have strong highlights, they're not offset by a darker region behind them, nor is there an opposing lighter side. 
• eyelids: most figures have problems with the edges of their eyelids. they're either too thin or too thick, too flat, or just plain invisible.
• clothes: if they're dynamic, it's easier to fix certain errors in post than tweak the simulation.  if they're conforming, there's almost definitely problems.  and both often have small poke-through issues. 

just to say, since using mostly raytraced shadows and final resolutions of 2400+ px, my render times have gone up as high as 24+ hours.  so if i find a small error that i couldn't see at test render resolution, i tend to just fix it in post.  you might be surprised at what can be hidden at even half of that.