I tend to avoid the rank and file height, weight and attributes are usually described as has been mentioned before. They seem out of place, with numbers being the worst of them in that unless the numbers are being explicitly read in some format - say a medical document or official format - they fail to "mesh". Vagueness sort of works better in these regards, or at least comes across as more natural; "A head taller than many a man." "Uncharacteristically muscular for a woman." "The firm sternness of an aged face pocked with a rough, short beard." 

None of these examples give explicit details as to what you're reading about - leaving it mostly up to the reader's imagination - but they tend to get brought up again later on... sometimes by [i]multiple characters in a row[/i], which leads to a really strange trend where [i]everyone[/i] notices the same thing... [i]and[/i] mentions it one after another. Even more amusingly this can result in where perceptions of a character change post to post, not by fact but sheer opinion as you noted; "tall" is what to someone who is six feet in height? Is the comparison known previously? Hopefully it was in the character sheet.

The reason it tends to get forgotten or repeated? I believe it is, by and large, relevancy. If a responding player does not consider the detail truly that important to their character or themselves, which is often a consequence directly related to their level of roleplaying and maturity in it, it flat out gets dropped. Sometimes this even happens to the responding player's character who magically change features with no apparent reason short of retroactive continuity, be it intended or not.

Either way, my rambling over, I appreciate "effective comparisons" like the examples I noted. They give the sort of sensation that you can generally picture and "know" what the writer is trying to say without explicit, almost mechanical details.