I love Macs and I have an entry-level iBook as my second computer. The downsides are that it is an expensive laptop for its spec and that software for Macs is thinner on the ground and more expensive. Having said that, there are free things you can use - there's a port of OpenOffice to Mac and there's Nvu for web design, for starters.
Upsides of a Mac: beautiful, stable OS (I've had my iBook for nearly two years and it's never crashed on me), works straight out of the box, comes with useful software pre-installed, easy to add to a network, no viruses or spyware.
The OS looks a bit different to Windows and uses some different terminology but it's not very different in practice.