My system has been online with Jabber for 7 days 8 hours and 35 minutes and the Jabber application has performed 80,278 Reads, and performed 6,752,493 writes.
To see this data for yourself, open Windows Task Manager, click the processes tab. From the View menu click on "Select Columns" and add check boxes next to "I/O Reads" and "I/O Writes".
I would be interested to hear the results that other people see from their Jabber clients. If you do respond with your results please fill out the below template, please include your Jabber version, system up time (Performance tab, "System" section under Up Time).
While that sounds like a lot of writes, consider this:
On my Windows 7 x64 system, Google Chrome has well over 3 million reads and 3 million writes in a 2 hour time span. Compared to Chrome, Jabber doesn't look very write-intensive. Jabber for Windows is at about 54,000 writes, but I only started it up about 15 minutes ago.
Also, keep in mind that I/O Writes doesn't refer to a single write operation (like save a document). It refers to internal write operations, which could involve many writes for one call to write something to disk.
Just a wild guess, but it looks to me like Jabber for Windows does some writes every time there's a presence update for a contact.