Well, that all depends what you want to do with your images. In theory the more resolution you get the better the image, but that's only true if the next generation CCD is equally as good as the previous but at higher resolution.

What does this mean for the size of output?

(gray size values are print sizes at 300dpi)

The above diagram is supposed to demonstrate the difference between the primary camera resolutions available in current (and upcoming digicams).

Megapixels	Resolution	Ratio	Print size @ 300dpi	Example cameras
0.8	1024 x 768	4:3	3.4" x 2.56"	Sony FD-91, Canon PowerShot A5
1.3	1280 x 960	4:3	4.3" x 3.2"	Nikon CP900s, Oly D400Z
1.6	1536 x 1024	3:2	5.12" x 3.4"	Kodak DC260, Canon Pro70
2.1	1600 x 1200	4:3	5.3" x 4.0"	Nikon CP950, Oly C2000Z

(Note there are other resolution cameras between these more common sizes such as the Sony D700 @ 1344 x 1024, but they would make the diagram to complex to understand)

As you can see as we get progressively up the megapixel scale larger and larger steps are required to effect a larger change in output size. To get TWICE the resolution of a current 1.3 Megapixel (1280 x 960) camera you would need 4.9 Megapixels (2560 x 1920).

Print size is given at 300dpi, although most modern Inkjet printers cannot actually output at this exact resolution (closer to 150dpi).

It's also worth noting that there is alot more involved in the ability of a camera to take good photographs than just the number of megapixels. A good camera is made up of a good, high quality CCD (no matter what the resolution), good lens systems, good electronics (primarily CCD amplification) and onboard software.

It's a shame that the 2 megapixel mark was seen as such a breakthrough, it was less so than the megapixel mark, however with each new generation of cameras image quality does improve as do features which make them more attractive than the older cameras, as far as image quality is concerened we have too few samples to make any firm comments.

UPDATE: Thanks to Geoffrey Faraghan for pointing out that the next real steps in digital photography CCD size will be:

Megapixels	Resolution	Print size @ 300dpi
3.1	2100 x 1500	7" x5"
7.2	3000 x 2400	10" x 8"