If I am to build another arcade cabinet, I would do a few things differently.  First, instead of using 1/2 inch thick plywood, I would use 5/8.  With 1/2, its tricky sometimes to screw the pieces together without missing the wood.  As well, 1/2 plywood is somewhat warpy.  So, probably best to spend an extra 50 bucks and get the 5/8.

The 20" TV I used is pretty good, but I would use a 23" or even a 25" next time.

More processor power means more higher end games you'll be able to play.  For instance, using a Pentium 2 @ 350 Mhz, I am unable to play alot of games made beyond 1998.  Preferably - use a box running @ 1 Ghz or better.