Great job, it reads very well, and has links to all the appropriate sites.
However I do have some suggestions. Going through top to bottom:
* In the "looking better" category, it's probably worthwhile explaining the new options in the GL renderer. All of the controls there have context-help if you leave the pointer over the label for a second, just summarize the functions here. Same in the Using MacMAME>Renderer section.
* In the "running faster" category, one important note for vector games is to lower the display resolution in the System Preferences before starting the game. Vector games always run at the full current resolution; this can be quite CPU intensive at high resolutions (2560x1600, anyone?)
* Also in the "running faster" category, it's probably worth mentioning that some newer games (Cruis'n USA etc) will not run at full speed on any existing computer-- even though an equivalent quality native Mac game might run flawlessly on the user's Mac. MAME's focus is on accurate emulation, not playing speed-- sometimes all you can do is wait for faster hardware.
About Roms>Rom Files
* In the "doesn't come with any games?" category, you list Robby Roto and Gridlee. PolyPlay is also listed at http://www.mame.net/downmisc.html
* In the "What is BIOS" category, your list is outdated. My list has acpsx.zip, atluspsx.zip, atpsx.zip, cpzn1.zip, cpzn2.zip, cvs.zip, decocass.zip, hng64.zip, konamigv.zip, konamigx.zip, macsbios.zip, megaplay.zip, megatech.zip, neogeo.zip, nss.zip, pgm.zip, playch10.zip, psarc95.zip, skns.zip, stvbios.zip, taitofx1.zip, and tps.zip. There may be even more now in 0.87, I'm not sure.
About Roms>Parents, Clones, and Merging
* You mention the "Attach Clones" menu item. I'm pretty sure this no longer exists.
Using MacMAME>Video Tab
* The "Use 16/32 bit color" popup was removed in 0.87a. That functionality is no longer required, and was breaking several games such as NeoGeo-raster. Screenshot needs to be updated.
Using MacMAME>Misc Tab
* The two "Don't Display..." checkboxes aren't described. Screenshot needs to be updated.
* I believe that the "While I'm playing a game that uses the mouse" problem no longer applies in 0.87; Carsten's patch to capture the mouse should fix this behavior.