Freelance Switch just published an interesting article touting the benefits of weekly freelance gigs over longer-term projects. I'm not sure that I agree with this. As I said in the comments, right now I'm finishing up a project that pays me weekly (which is awesome, don't get me wrong), but most of my regular clients pay monthly. And when I'm writing for a website or magazine, I get paid even less frequently than that.
This makes my budgeting a little less predictable, but it also gives me greater flexibility. If I had a regular gig with mini-deadlines every day, then it would make it a lot harder to write queries or pursue other projects. Right now I have three clients who pay me for a set number of blog posts per month, but it's up to me when I write and publish those blog posts (though I try to spread them out evenly over the course of the month). This arrangement works well for both of us, because they don't have to worry about blogging and I can schedule it around my other projects. Or I can take a day off without much interruption.
Invoicing (and the follow-up email that it often requires) is probably one of my least favorite parts of the job, so invoicing monthly makes more sense for me. I'm betting that my regular clients wouldn't want to deal with weekly invoices either, because they're busy running other aspects of their company.
Bonus! Kristen King at InkThinker is giving away 3-month accounts with Infotrak Invoicing and Steph Auteri at .Freelancedom* reviews 7 invoicing applications.
So, how often do you invoice? Do you use an online invoice service or just good ol' Word documents?