I had WordPress set to the “display -4 off from GMT” and it was causing problems in a couple of areas:
1) I’m in an area that uses (unfortunately) Daylight Saving Time so being a fixed number of hours off from GMT wasn’t really working too well anyway.
2) It horked up Semagic’s editing of existing posts. This isn’t really Semagic’s fault per se (MetaWeblog contributes to this), but it does contribute to the problem. Semagic happily uses the local timezone when it creates a post.
<methodcall><methodname>metaWeblog.newPost</methodname>
<datetime .iso8601>20051227T16:04:53</datetime></methodcall>
IMHO, it shouldn’t – really, nothing should ever send a non-GMT datetime over the wire – always send it GMT – if the other side needs to do timezone conversion, so be it. In this age of SOA, it’s just silly to think that the client and server are generally in the same time zone, and synchronizing on “GMT over the wire” makes life easier for all involved (much like how we standardize on network byte order, for instance).
In any case, I’ve locked down both sides of this to GMT to make life easier on me (again, really both should be GMT-only over the wire). 
locking Semagic down to GMT was equally simple, thankfully, since it has a setting for that:
[Edit 2005-12-29]: It’s been fixed in Semagic build 1.5.6.5 and is now GMT over the wire
