By far the easiest method that I've come across is setting my preferred email client, Mozilla Thunderbird, to check your email using IMAP. With IMAP, your email is stored online (whereas with POP, your email is normally downloaded to your machine).
For the Double Cloud Whammy, I can recommend using Google Apps to host your web site's email. This way, you can check your email using Google Mail via a web browser, or an email program on your PC. Because you can sync your data using something like Ubuntu One, there's not a problem if you have multiple machines. Currently I have 3 computers. But I'm not bragging.
So, these are the steps required for The Google Mail-Hosted IMAP Email Anywhere Experience:
1. Sign your web site up for Google Apps Standard.
2. Get your web host to recognise you're hosting your email with Google Mail. With DreamHost, there's an easy checkbox option. With Rochen (who I host all my business sites with) I had to use cPanel (Mail -> MX Entry) to add the MX Entry aspmx.l.google.com.
3. Configure your email client to work with IMAP. It's pretty easy with Thunderbird, and there's some handy instructions over at Google Help.
4. Set up Ubuntu One or grsync to synchronise your .mozilla-thunderbird folder, so that everything works across all your PCs.
If you are using Thunderbird as your email client, you can download mail using File -> Offline -> Download/Synchronise Now, so that can look business-like and not have to talk to anyone on the commute into work.
That concludes my meagre offerings to working with the Much Hyped Data Cloud. Next up, some good old-fashioned and opinionated polemical pieces ;)