[usaftrevor]

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So what is the difference between PAHUD showing me that a player is 23/3/5 and knowing that Frank is tight, aggressive post flop and rarely raises PF and generally only big pairs?

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you said the difference yourself: PAHUD shows you. You don't have to remember it. Other diffrences include but are not limited to:

fewer hands / hr in live games
higher rotation of faces you've never seen before and may never see again (in a casino)
those that you do recognize, if they're worth remembering, they'll probably remember you, too - and adjust.
[and mentioned already...]
alcohol abounds
a seat at the poker table is no different from a seat at a table game to many gamboooolers. this is the kicker right here. biggest reason why live is so much easier.

and then you've also got consider all the reasons recreational players pony up to the table... just for the competition, kill time, maybe they just hate money...

live poker will have its ups and downs, but i don't see it fading into the distance any time before the sun burns out.