Rivet Joint - Your constant bashing of BOH on here is getting a little tiring, yes there is of course a notable element of risk starting a base 30 miles from one of BE's largest (been overtaken by BHX in the last year or so) bases where they essentially have a monopoly. However equally I'd have some confidence in Flybe's current management, which a lot of previous experience coming from Easyjet, not exactly an airline known for cocking things up on a regular basis.
As for the whole 'no one wants to fly from BOH they should just make it a housing estate' that is frankly rubbish, because despite a smaller catchment and significantly worse transport links than SOU it has still managed to attract ~650,000 pax per year, not to mention the notable number of non passenger business's operating from the airport (i.e. cobham, paintshop, scrappers, based light aircraft etc). It also has a far more useful runway length, and can handle more than 2 A320 sized aircraft at any one time!
As for previous failed ventures most have fallen into two categories, unknown/not established operator or an inappropriate frequency/aircraft type (i.e. BE's middle of the day MAN, SI 3x week to JER vs 3x day up the road, FR using 738's to PIK etc).
With a bit of luck both airports will benefit from this move, with BOH being able to broaden their routes beyond the bog standard bucket and spade ones and SOU getting a kick up the rear to reduce charges/improve the airfield/not be so reliant on Flybe.