i've been using it since 7000, and noticed a few bugs.
7100 had issues with network share permissions randomly dying (only on some systems, and a format would fix it)
7127 has a funny bug where upload speeds are shown as double what they really are (i can upload 250MB/s on a gigabit connection, lol)
7264 i think, has data corruption issues
thing is, theres really only one problem or so with each build - once MS pick one without any bugs like this, we'll have a great OS. I'm using 7127 cause its only a bug, not a critical fault - i can live with its flaw.
Overall the OS is faultless. you have the usual rage that things you liked are moved somewhere else, or hidden... but after a few months you go back to vista and you miss how 7 did it.