FWIW, HP-UX and Solaris also have ACK avoidance heursistics - they have 
a Mentat history - although both should be pretty good and neither 
should hold-off ACKs for two seconds...

IIRC the last time I looked at a packet trace from a link with LRO 
enabled under "Linux," that too caused "ACK avoidance" - that is we 
stray from the "ACK every other" faith.

rick jones