biochemistry - Simple diffusion of lipid-soluble molecules through phospholipid bilayer -- does anything get "stuck" in transit?

I think, given Alan's answer the question you might be asking is something like
'do compounds become concentrated in the lipid bilayer', as opposed to achieving high concentration inside the cell after diffusing through the membrane as he describes.

This could certainly happen (if that's what you're thinking), but usually won't for I think two reasons.

The first is that any molecule that would not soluble in the interior of the cell is going to have a correspondingly small not going to be found in the blood or lymph, tissue, ocean or other milieu the cell is living in, which will be mostly water.

You might well ask whether there are cases where the compounds in question might be available in low concentrations around the cell and over time accumulate in the lipid bilayer. This slow concentration model probably happens, but there is a compensating mechanism - the lipid bilayer is taken into vescicles and degraded, to be replaced by newly synthesized such that membrane components renew themselves. This process includes the cell engulfing by endocytosis and specifically turning over membrane proteins.

The turnover rate for most cells is on the order of days, some of the best numbers for this are behind a paywall, but a reference to synaptic membrane turnover shows some components turn over varying between 6 and 24 days. Different components such as cholesterol, phosphatidylcholine and phosphatidylethanolamine have differing rates of turnover.

So between these two effects, the concentration of 'permeant molecules' would be low for most cases.