1.8 Saw a lot of awesome features, but also a few unfortunate bugs. 1.8.1 aims to fix those bugs!
Please note: 1.8 is explicitly compatible with 1.8.1, meaning you do not have to upgrade servers in order to have 1.8.1 clients join your server. However, it is strongly recommended that you upgrade anyway, as huge performance improvements are part of this bugfix batch.
UPDATE: PRE-RELEASE 2 FIXES THE FOLLOWING:
Cross-platform server jar: https://s3.amazonaws.com/Minecraft.Download/versions/1.8.1-pre2/minecraft_server.1.8.1-pre2.jar
Cross-platform server windows exe: https://s3.amazonaws.com/Minecraft.Download/versions/1.8.1-pre2/minecraft_server.1.8.1-pre2.exe
Credits: Mojang Team