Mini cruise anyone?

I was out the other night with my family celebrating a relative’s birthday.  While we were out the topic of cruising came up.  My cousin did his first cruise in May this year and has got the bug.
He is only 19 and was asking me about short cruises where he can go with a group of friends for a boozy weekend rather than going out into town.  I also had my Uncle asking what short cruises are going next April to celebrate a wedding anniversary.  I think that the mini cruises are certainly a good idea for a celebration or for a group of friends.  When I was last on a mini cruise I couldn’t believe how many hen parties were on there.  Mini cruises seem to be the big thing for a good weekend away.  It gives people chance to experience a cruise if they haven’t cruised before and also for people who are regular cruisers to experience different ships.  Most of the mini cruises tend to be for 2 nights however there are also 3 and 4 night cruises sailing from the UK.  When you think of what you get included in a cruise it would probably cost you more for a weekend somewhere in the UK than it would to cruise.
I came up with a few options for my family for what they were looking for but there are lots more mini cruises out there for 2012.  Here are some of them I found

Independence of the Seas
2 May 2012 for 3 nights from Southampton
Starting price £299pp

P&O Ventura
23 Mar 2012 for 2 nights from Southampton
Starting price £299pp

Have you done any mini cruises?  How did they compare to a longer cruise you have been on?