With the death of my Palm Treo phone, I have migrated "to the cloud," initially using an HTC Dream/G1, running a customized version of the Android platform called CyanogenMod .
I since purchased an HTC Legend, which is massively better provisioned for memory and CPU than the Dream. Unfortunately, it has proved prohibitively troublesome to get it to run CyanogenMod, as the built-in firmware is quite uncooperative with the requirement to replace said built-in software.
CyanogenMod is a free, community built distribution of Android 2.2+ which greatly extends the capabilities of relevant phones. This includes both minor and fairly major "tweaks" and extensions to the software built into the platform, substantial efforts on performance optimization (so that it works fairly well, even on an ancient HTC G1), and inclusion of interesting free software into an overall software distribution (not unlike the way the Linux kernel is assembled, along with a cast of supporting software, into a Linux distribution.
Nightly Dream/Sapphire builds of CyanogenMod
Sadly, no longer being built nightly, as the maintainers have moved on to bigger and better new phones.
Allows you to transmit URLs from an Android device to a desktop web browser (specifically, instances of Google Chrome.
I'm taking a look at Android-based tablets to provide something bigger than a phone and more portable than a laptop
Not useful, but entertaining; let your phone display what looks like the DOS Boot display.
I don't agree with all the choices, but there are a lot of interesting apps listed here.
Some Android devices are easy to customize to run your own firmware. Others, not so much. (My HTC Legend turned out to be in the "not so much" category, sadly.)
A somewhat peculiar thing about the newer "PDA" platforms is that the built-in capabilities for note-taking are rather limited. This contrasts, for instance, with the Section 2 platform where "Notes" were a basic built-in feature.
Some interesting web services have emerged.
Nevernote - An Open Source Evernote Clone
This is a desktop application written in "Java" which interoperates with the web service, Evernote, which offers clients running on common mobile phone platforms.
A mode for Section 2 that interacts with the service.