I made the attempt. No one can fault me for that. However, I was defeated by the twisted, anarchic madness that is the ARIN database.
A step back: I was considering refining the GrabIP database to more accurately reflect the true countries where IPs are used.
APNIC, LACNIC and AFRINIC are all sanely managed. Countries and IP blocks are accurately mapped. RIPE gets a little messier, but there is no real problem with it. Just have to watch out for the blocks tagged as EU instead of their host countries.
ARIN is complete madness. As the only IP registrar on the block for a long time, there are a number of archaic nooks and crannies to watch for. Like this gem: 65.165.84.11.

OrgName:    Sprint
OrgID:      SPRN
Address:    12502 Sunrise Valley Drive
City:       Reston
StateProv:  VA
PostalCode: 20196
Country:    US
NetRange:   65.160.0.0 - 65.174.255.255
CIDR:       65.160.0.0/13, 65.168.0.0/14, 65.172.0.0/15, 65.174.0.0/16

Nothing too earth-shattering here…but wait, there’s more information!

OrgName:    COMMUNICATION ENTERPRISES LTD
OrgID:      CEL-30
Address:    KM # BLVD DEL NORTE
City:       SAN PEDRO SULA
StateProv:  SAN PEDRO SULA
PostalCode: 00000
Country:    HN
NetRange:   65.165.80.0 - 65.165.87.255
CIDR:       65.165.80.0/21

A whole chunk in the middle is assigned to a company in Honduras? Oh great, so now I have to write exceptions to weed out the child CIDR blocks that are in completely different countries.
Needless to say, this attempt to refine the data lost its appeal quickly.
Just using the high-level data in the GrabIP database, it is clear that there is still a great deal of overlap in the ARIN data.

code	country			NUMBLOCK
US	UNITED STATES		30935
CA	CANADA			 4903
PR	PUERTO RICO		   29
GB	UNITED KINGDOM		   24
DE	GERMANY			   22
JM	JAMAICA			   18
BM	BERMUDA			   17
FR	FRANCE			   13
JP	JAPAN			   12
BB	BARBADOS		    9
CH	SWITZERLAND		    6
HK	HONG KONG		    5
NL	NETHERLANDS		    5
SE	SWEDEN			    4
IT	ITALY			    4
NO	NORWAY			    4
BS	BAHAMAS			    4
BE	BELGIUM			    4
VI	VIRGIN ISLANDS, U.S.	    3
ES	SPAIN			    3
AG	ANTIGUA AND BARBUDA	    3
AU	AUSTRALIA		    3
CZ	CZECH REPUBLIC		    2
SG	SINGAPORE		    2
DO	DOMINICAN REPUBLIC	    2
FI	FINLAND			    2
LU	LUXEMBOURG		    2
IE	IRELAND			    2
MX	MEXICO			    1
AT	AUSTRIA			    1
LC	SAINT LUCIA		    1
TR	TURKEY			    1
PL	POLAND			    1
LB	LEBANON			    1
GD	GRENADA			    1
HU	HUNGARY			    1
IL	ISRAEL			    1

However, when I originally started this project 2 years ago, some of the blocks for Iceland were listed as ARIN. Now, all of Iceland’s blocks are in the RIPE database.
Hopefully in the next year, the registries can get the counrty assignment mess sorted out.
A sidenote: Right now, ARIN is still the biggest fish in the sea.

arin	36051
ripencc	14588
apnic	10445
lacnic	 1457
afrinic	  437

Maybe I should post the Weekly Breakdown of IP Blocks by registry and country.