I'll definitely be buying the new edition. While I tend to agree, in general, with St. Nougat that there are things that I dislike about 4th edition, they definitely muddied the water in some otherwise key areas, and changed some rules in new and surprising ways. Notable examples: the dodge skill was basically ruined in 4th, Melee was completely changed in 4th (used to be able to damage on every combat round), the Shifter rules were written so poorly as to be unreadable, and many more...
On the other hand, there are some things that I like a lot about 4th edition. The improvement curve on technology is quite interesting. Given the improvements that we've had over the past several years, here in the real world (real micro-drones, the upcoming Samsung flexible cellphone) I think 5th edition is going to have some leaps and bounds to keep up with the 60-year time shift, and I am really looking forward to seeing how they deal with that! Similarly, the time-curve of improvements in Magic has been exciting to carry forward, and I am really looking forward to seeing what they come up with there too!