Sets could do with re-ordering, from the most recent stats (though they are not very recent):
http://cap.smogon.com/ShoddyStats/2009-05/CAP-200905-Details-Little Cup.html
Sash has over 84% of all use, Scarf with 7% and all others not enough to be shown. Also roughly 1/3 of Digletts were used as leads.
I would advise pretty much the reverse of the order you have now, with Choice Revenger Killer last and lead first (or possibly second).
Pursuit should be moved to OO, its quite situational and not a move you want to be trapped in at all. Its just free setup for Croagunk, Gligar, Houndour, ect...
Focus Sash should be the main item on non choice revenge killer, the loss of power is worth getting to attack twice almost every game and the stats back this change up (LO was too low to get into them). Some parts of the comments will need changes to reflect this. Also, remove Night Slash from this set as diggy can;t learn it.
OO could mention SR as a possible on non lead diggy, and HP Ice on lead diggy. They are not the most commonly used combinations, but can work reasonably well.
Not going to do detailed suggestions for the comments, but they look pretty good overall, other than maybe the Opinion which could do with more substance. Diggy is a Pokemon that moulds much of the LC metagame, and one of the three 20 speeders, but it does not have much raw power at all. Sure you can find more things to talk about.
Gligar and missy should be mentioned in Counters, Gligar is the reason most carry HP Ice but its still missing from most lead sets. SubMissy (or gastly) is a brilliant counter to any set lacking Shadow Claw, or to a lesser extent Rock Slide/Pursuit. I think Duskull works well to with W-o-W, not sure but I think it could take a single SC. sbc suggested Mantyke for counters, that works well. Staryu can handle a EQ and easily 1KO back. Porygon can trace you and KO with Ice Beam, but will not like two STAB EQs in the face. Paras is good against most varients, as is Shroomish and Bulbasaur. They are hurt by HP Ice or EQ but not too badly.
Maybe worth mentioning in team options that keeping SR off your side of the field (either with a anti SR lead or spinning) will really help Diggy, especially if you run Sash.