The answer is that there is no quick answer to this question. The only real limitation is how long the server will allow scripts to run before it times out. The timeout issue is determined by the web server software and the PHP settings. By default, many servers will timeout after thirty seconds.

Therefore, the number of feeds you can add depends on how many entries the feeds have, how often it is updates, how powerful the server is, and how you configure autoblogged. On a shared host we wouldn’t recommend running more than 5 feeds at a time. But with feeds that aren’t updated much you can add quite a few more, because most of the work isn’t checking the feeds for new articles, but when it has to actually process those new items.

One thing to consider is that WordPress already has quite a bit of overhead, especially on a blog that gets a lot of hits. Because the work required to retrieve feeds, process the xml, create tags, and add posts is significant, you should always be careful with adding too many feeds. A busy WordPress site is already a big load on the server, so you need to consider the extra load required to import the RSS feeds into WordPress.

If you want to set up more than 5-10 feeds, we recommend offloading part of the processing using an external application such as Yahoo Pipes, mysyndicaat, or feedrinse to aggregate the feeds and do any necessary filtering there. These tools will output a single aggregated, sorted, and filtered RSS feed that you can use with AutoBlogged.

That isn’t to say AutoBlogged can’t handle more feeds. We have seen a number of installations with 30-50 feeds that worked perfectly. As we said before, it really depends on the feeds you use. A feed with dozens of posts a day will always require more processing that a feed with only a few posts a week.