Extracted from  "GCBASIC Command Guide.doc":

Random Notes:

• When dealing with system registers, the variable name may be omitted and only the bit specified. For example, SET ADCON0.ADON ON is identical to SET ADON ON.
• GCBASIC is not case sensitive – for example, Wait, WAIT, wait and WaIt would all be treated identically.
  

Known Limitations:

• Chip Speed: 0.1-60 Mhz
• Lines of GCBASIC code (including subs): 20000
• Assembly Program: 20000 lines
• Include files: 25 (includes built-in include files)
• Constants: 400
• Variables: approx. 3800 or available RAM on PIC (whichever is less)
• Subs (including in include files): 500
• Array size: 80 bytes on 10/12/16, 255 bytes on 18 (Avoid large arrays wherever possible)
• String length: 20 characters default, 80 if declared using DIM
• Strings: 500

Things which MUST be defined in EVERY program:
#chip model, MHz
(These can be defined in an include file instead. If something is defined in an include file and the main program, the definition in the main program will be used.)