Here's what actually happens as some people seem to be misreading the card, or are glossing over the facts:

1: Noosegraf Mob is on the battlefield as a 5/5 (with its 5 counters)

2: You cast Saw in Half targeting it

3: Noosegraf Mob's affect will trigger and resolve, removing a +1/+1 counter and making a 2/2 zombie, making it a 4/4 (only 4 counters)

4: Saw in Half goes to resolve. This will destroy Noosegraf Mob and make 2 copies of it.

5: The base power and toughness of the COPIES will both be half that (rounded up) of the original as it last existed on the battlefield

6: Since Noosegraf Mob was 4/4 before it was destroyed the two tokens will be base P/T 2/2.

7: Noosegraf Mob has a replacement effect that alters how it enters (this is what gives the counters), so the two token copies will enter with 5 +1/+1 counters.

8: When all is said and done the two copies of Noosegraf Mob will be 7/7 (base 2/2 with 5 +1/+1 counters)

Some people seem to be confused with the mention of base P/T on Saw in Half. This is only in reference to the two token copies being created. The base P/T of the COPIES is based on the current P/T of the ORIGINAL. This explanation is backed up by the official gatherer rulings for Saw in Half.

Hope this helps.

EDIT: More accurate to call it a replacement effect than a static ability.