I get the impression from people that Wacom is to digital tablets what Adobe is to digital drawing - they'll tell you that you just don't have to bother with the other brands (sorry to any Corel enthusiasts out there, but you'll humour me on that one). Having got my first Wacom I'm comfortable with that idea.
This is such an intuitive device and within minutes of mucking around on Photoshop I'd put away my mouse. Even though I'm a bit stupid, the tablet's buttons I could use instinctively after an hour or two. I'm an illustrator who employs detailed/fine pen & ink drawing and I was very quickly able to replicate closely the way in which I draw on paper, which had been my main concern. An important factor in this regard is the replaceable nib. My accompanying pen was packaged with several harder plastic nibs but included one "felt" version, which is made of compacted fibrous stuff and grips the tablet surface better, making it feel more natural and providing more accurate control for the starting point of every stroke. The only downer is you can't get them separately, though you'll get five in a pack with varied nibs but these are a bit pricey. See the Wacom website and other online sellers.
This rather attractive thing will save a great deal of time in scanning etc, and don't forget it's great to use the pen with the tablet's buttons to navigate around browsers and documents. As a left-hander who has always, for some reason, used a mouse right-handed (I don't know, is that normal?), my mac feels much more tailored to me. And let's be honest here, I am the most important person in the room, after all.
Lastly, unless you use expansive movements when drawing, the A5 size should be big enough, so you won't have to fork out for the bigger ones.