Software differences?
If you can possibly the best thing to do is to get down to an Apple Store and take one for a test drive. Safari (the web browser), iTunes and iLife (iMovies, iPhoto, iWeb and iDVD) all come pre-installed and will probably cover most of the things you'll want to do day to day so try and have a look at them.
In terms of how it "feels" compared to Windows, well it all feels very integrated. It's easy to make a DVD up from your movies, with your photos on the menus and music from your iTunes library.
The user interfaces all feel very slick and polished. Windows XP looks ugly in comparison and while the upper versions of Vista try for a similar effect it feels crude and distracting.
I think that basically I enjoy using my Mac to get things done, which is something that I just can't say about Windows.
However if you're one of those people who's likes installing lots of games and utilities from the internet to have a play with then you'll have problems with your Mac. Yes those sorts of things exist but there is just so much more software out there for Windows.
You'll also hit some "snags" with Office Documents and you'll come to realise how many people either email them around or have web sites where you download them from (a real pet hate of mine).
TextEdit, which comes with your Mac, will do a pretty decent job of opening up most documents but things won't look quite right.
You can get better applications either for free (OpenOffice) or bought (iWork) but even they will still throw the occasional wobble opening up Office Documents.
You can then go and spend a lot of money getting Office for your Mac but personally I really don't think it's worth it.
Basically for most day to day tasks the Mac will come with what you need and you'll the applications far better than what a PC will come with.