To give it a fair shot, I checked out drop box and set up the GMail push services. For me, the set up doesn't work well. To use GMail push for calendar, contacts & mail, I need to use Exchange and had to delete the email for one of the companies I freelance for. I don't always keep it there but when I'm working on a job for them, it's handy. But as far as the GMail/ActiveSync service itself, yes, it works just like MobileMe it seems.
But I also don't use push for email unless absolutely necessary (when I'm working on a job and I'm on location, etc) so it's not worth it for me to loose the exchange setup just for GMail.
As for DropBox, I've been hearing so many good things I decided to check that out as well. Very nice service. Syncs well & integrates well. It does a good job of replicating iDisk. But to get more than 2GB free a month, which I would definitely need, it's $9.99/mo for 50GB so the cost is actually more than MobileMe at $119.99/year and 50GB is more space than I need. And that's all it is...space. And I can bump up to 40GB on MM for $150/year but I don't need that.
I'm not knocking the alternatives, I just wanted to actually compare. At the end of the day, it seems using either method works similarly and setting it up is not complicated or "cobbled" together...really just 2 pieces rather than 1. It just depends on what your personal needs are.