Couple of things. 1. Hardware - if you have a good keyboard and good wireless mouse, hang on to them and use them with the Mac - the Apple products are, to say the least, pretty bad. 2. Software - check out the programs you use most frequently to find out a) whether a Mac version is available and, if not, b) whether a viable alternative exists. For example, I've failed to find an html editor that matches Homesite - and I've tried them all - and replacing things like Photoshop with the Mac versions can get expensive. So I use VMFusion and have a virtual Windows machine on the iMac. Since discovered there's a free alternative, VirtualBox.
In general, though, go ahead - you'll enjoy the difference and the almost total lack of those kind of notices that say, 'Sorry we have close now, would you like to send a report to Msoft'