If you had a UMPC or netbook, would you use a basic instant on operating system? The new Sony Vaio P has this feature as the first "pocketbook" netbook. It probably won't fit in most pockets, but it will slide nicely into a clutch purse.
Most instant-on operating systems run a simple version of Linux. You'll have your e-mail, your web browser, your contacts, and a few other basic things. The HTC Shift was one of the first netbooks to have an instant-on interface called SnapVUE. I'm not sure how many people really found it helpful since you may eventually need complete access to all your applications. By then, you've booted into Windows XP or Vista.