Hi there,
On the home page of one of our web sites we embed a .swf file which is essentially just marketing.
Typicaly in the past they've been about 300kb, but the designer has passed us one to put up that is a little over a 1MB.
What are the performance concerns with this? What should be used as a max size for these if there are concerns?
The only performance concern here is how long it takes for your users to download the SWF. Large SWFs are fairly common ever since the introduction of Adobe's Flex framework. I recommend that the SWF has some sort of loading indicator and that caching is enabled for the page. After the SWF is in the user's cache, it loads instantly on subsequent visits.