Ok, I just made sure before I posted that my CSS is valid, as is my XHTML.
If you visit my site in Firefox, the last post is pushed over to the right for some strange reason, but this only appears when they're classed as 'asides' (using an implementation of matt's asides).
I can't see what's wrong with my generic list code to cause this to occur, hence it must be some padding/margin issue. Yet playing around with the web dev toolbar and changing suspicious values hasn't helped me solve the problem. I've only posted a few entries since I've been redesiging over the weekend, thus I didn't notice anything was amiss till now.
Looks fine in Opera and IE.