Well, I'm on Gmail now. I got an invitation the other day and took them up on it. I'd gotten an invitation before and didn't follow up...
It's great. I really like the convenience of web mail. I use 3 or 4 different computers and it's nice to be able to check mail really quickly. Gmail is by far the best web mail program I've ever used.
I think the model with labels and starred email for the stuff you are currently working on is good, but I'll have to use it awhile to see. Good search will be a help once I have enough of it... I think. Keeping things in linear conversations is a good way to go also.
One thing that's annoying. It's been down a couple of times recently. If it happens a lot, that'll be a big downside, but I'm willing to wait and see before I pass judgement here. It could well be that I've just started using it when it had a few problems.