Bethesda has lifted the 100MB restriction on mods for Skyrim, and it's now being beta tested.
The unlimited size is part of an update to the PC version's Creator Kit (1.9.33). The Creator can be beta tested via Steam (click on the source link below for more info), as can the Skyrim Launcher. The launcher no longer downloads mods from the Steam Workshop – the Steam client will do it instead.
[Source: Beth Blog]
Skyrim has been out for a while, but given gamers' persistent love of mods for the title, this is great news for a lot of modders.