Back in March 2006 some changes were made to this bad junction. And to be honest the traffic flow has improved in the early morning rush hour, but I don't have any evidence for a causal link.
* northbound side of the roundabout (over the M27) is now three lanes.
* southbound side of the roundabout (over the M27) is now two lanes, with a new set of traffic lights controlling traffic going straight on (onto M271 towards southampton) or right (onto M27 slip westbound).
* westbound slip off the M27 up to the roundabout now starts earlier, meaning no hard shoulder for some distance on the M27 (a blue sign announces this).
* no longer a dedicated slip at the roundabout from M27 westbound onto M271 southbound - instead all traffic coming off M27 is controlled by traffic light at the top.
* Its still a busy junction, but I think its a little less "bad" than before. I'd give it a bit more time though.
The slip down onto the M27 eastbound is still ridiculous: two lanes off the roundabout go into one before joining the uphill motorway, lots of lorries from the docks & industrial estate... fun and games.