As for CPU mining in 1.5.x+, I find the rate of accepted shares is the same crap rate as previous versions, as far as CPU mining goes. It's no worse than it ever was, but the efficiency is higher (efficiency being accepted shares / requests, NOT the reject rate).
I can confirm 1.5.2 does not drop hashing speed anymore (Linux, Ubuntu 10.04, CPU mining only). I ran one all night and the speed is still as expected. My accept/rejects are reasonable unlike what others have reported. Here it is:
cgminer version 1.5.2 - Started: [2011-07-28 23:09:41]
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[(5s):6.8 (avg):6.8 Mh/s] [Q:1335 A:48 R:4 HW:0 E:4% U:0.08/m]
TQ: 2 ST: 2 LS: 0 SS: 0 DW: 1331 NB: 88 LW: 1517 LO: 0 RF: 0 I: 0
Connected to http://api.bitcoin.cz:8332 as user _________._____
Block: 0000082a6635d024f3914d9b6cb27760... Started: [09:00:19]
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[P]ool management [G]PU management [S]ettings [D]isplay options [Q]uit
CPU 0: [3.4 / 3.4 Mh/s] [Q:761 A:19 R:1 HW:0 E:2% U:0.03/m]
CPU 1: [3.4 / 3.4 Mh/s] [Q:758 A:29 R:3 HW:0 E:4% U:0.05/m]
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