Get the tides right and you should be fine. The slip is substantial too. Water skiers launch from there. I'm not sure if there's a stipulation of craft type / style to launch there, but the harbour authority should be able to clarify that for you.
With regards to the PWC users; the majority are actually a good bunch and do a lot, on a voluntary basis, to maintain the area and access for all water users. In fact, I wouldn't be surprised that had they not got involved then the local councils (Fareham & Gosport) would probably have let the slip go and eventually denied access, siting a lack of funds, man power or resources to keep it in a usable state.
They have a pretty comprehensive website: Solent Skiers
And you'll probably find this interesting reading (especially the licence bit): Parking, Slipway & Launching Info
All the best
PS. I don't ski, have never owned a PWC and have no intention to (running in boots for years killed my knees!), however, I think we need to give people the benefit of the doubt before making assumptions