some stats, but not for those applying for a spouse visa, but those applying for ILR, from 2006

ILR Grant/Refusal breakdown Totals
Granted 76,655
Refused 5,285
Other 13,450
Total 95,390

and

Settlement refusal Spouse*
- Refusal Marriage/relationship terminated or no
intention to live together 300

-Refusal despite domestic violence 220

Settlement refusal other than husband or wives
- Refusal no extension granted
167

Refusal premature application 715 *** warning don't send your app more than 28 days b4 you've been in uk 2 yrs or this happens ..