i am 5'8" too, and i love the way heels look but i, too, hate being so tall around others. plus my fiance is only a few inches taller than me to begin with, so adding heels makes us the same height!! i have found that kitten heels are a good happy medium, especially with pants because it's not so obvious that they aren't high heels. i've spent a lot of time shoe shopping for kitten heels that are still fashionable looking and in my price range, and i've had good luck with steve madden. they seem to consistently have some sort of kitten heel shoe available each season.for example, here's a pair i own (although i noticed online the leather doesn't look as shiny and nice as it does in person...but you get the idea). http://www.stevemadden.com/item.aspx?id=40522
I love tall women who wear heels. It's so glamazon. I'm 5'2 or 5'3 so I will never get to experience this! I definately don't think 4" is too much. That's a fairly standard stilletto height. I know a lot of professional women who wear 4"+, since obviously it's a trend in footwear for the past season or two to have towering heels and big platforms. That said, for a conservative law firm, I probably wouldn't go over 4", but I think this is a perfectly appropriate height.
I think the appropriateness of a particular heel height depends on the size of the shoe. Trust me... a 3 inch heel on a size 11 does not look the same as a 3 inch heel on a size 5. The angle of "steepness" is completely different.