SUPPORT BY KDENLIVE (0.8.2):
mts or m2ts files can be imported to kdenlive and put into the timeline. But they are quite heavy for realtime preview in kdenlive 0.8.2 at Core i5 M560 CPU at 2,56GHz and 4 Gigs of RAM. So use of proxies is reasonoble.
AVCHD looks like well supported in timeline edit, trimming and rendering in standard KDENLIVE 0.8.2 and MLT 0.7.6 package
In mixed config KDENLIVE 0.8.2 + MLT 0.7.7 (looks like MLT was installed from SVN ppa but KDENLIVE fror RELEASE ppa) there I faced some issues - video is rendered OK, but sound in trimmed clips (scenes) has jitter and down pitch. No matter what output format is.