I find iMovie 09 is fun and I know it will not work with Final Cut Pro X if I decide to buy next month. And what is the difference between two? I can't find new chart for both on Google search.
Too many differences to list. If you like iMovie 09 I highly suggest using iMovie '11 for awhile as it has more features and is a lot better overall IMO. Once you have reached your limit with what you can do with iMovie 11 then switch to FCP X. Final Cut Pro offers much more powerful editing tools and contains better color correction, sound editing, compound clips, and much more.
What do you want to compare? iMovie '09 vs. FCP X or iMovie '11 vs. FCP X?
Anyway, the difference between the two, is that FCP X allows much more advanced editing including effects and output options.
Have you taken a look at Apple's iMovie and FCP X websites yet?