No, you don't need PDAnet.

If your laptop has bluetooth, you don't even need a cable.

But please buy the laptop data plan.  Or use it very, very sparingly.

Verizon prices it's data with the expectation that people are going to
do this (almost $50 per phone).  $15 Sprint Vision is gone if everyone
starts using it for a laptop.

As mentioned you can use Bluetooth without any additional software or
patches (assuming the firmware is 1.12). Very easy to do, and the DUN
part is very similar to the cable option you are used to.

But if you do use PDANet (overpriced, IMO), you can then use your sync
cable to connect to your laptop (if you are running Windows). Since my
laptop doesn't have built-in Bluetooth (yes I have a dongle), and since
when I have my laptop my Treo's cable is generally in the same case as
the laptop, I actually might prefer using the cable. During my, albeit
brief, speed tests the cable seemed noticeably faster than Bluetooth.
This of course could be because my Treo's Bluetooth transceiver seems
about as powerful as a crystal radio's "receiver."

Now I won't feel guilty if I connect to my laptop because I was told it
was OK when I bought my Treo (without needing to change my Vision plan;
which happens to be grandfathered). I also bought my Treo after
Bluetooth DUN had been enabled, and instructions on how to use it are
right in my manual.

That being said, I don't think I'm going to have to use it much at all.
Even when I tethered my cellphone, it was only on rare
occasions--generally to send a quick email or two. Most of the time, I
use my laptop at a client's location (using their Internet access), in a
hotel with broadband access, or at an airport with WiFi (only if it's
free).

If I found myself in a situation where I had no other easy
access--generally at airports--and needed to reply to an important
email, I would tether rather than type out a crude reply on my phone
(email was forwarded to my Vision email account, so I could at least
check email on the phone). But again, this happened rarely.

And now that I'm using a Treo, I'm certain I will tether even less.
During my last business trip I used the Treo for email, even while in my
hotel room; and the hotel I was in offered free broadband. I was able to
shoot off a few email messages faster than it would have taken to
boot-up the laptop, login to the hotel's WiFi network (this one used a
proxy/password protected WLAN--you get a username and password when you
check-in).

Finally, I've had my Treo for about a month and a half now--and have
been using it a lot (Versamail set to auto-retrieve each hour, Pocket
Express set to do a full update each morning, Mobile TS to remotely
access a few servers/PCs, etc.). I just checked my Treo's lifetime data
usage (by "dialing" ##786) and it was surprisingly (to me) only 46 MB (I
connected to my laptop only to get it setup and tested--I haven't had
the need to actually tether). I don't know if my Treo's counter is off
(actually reads 46462 kilobytes), or I just overestimated how much data
I actually used (I had assumed at least 100 MB).