What needs to be addressed (in no particular order)

  The Mail Client

• The mail client is Ok, but is far from complete in my opinion.  There are virtually no options to configure the look & feel, delete confirmations, etc.  
• You can only select one email at a time, so moving or deleting a bunch of emails is tedious at best.
• HTML emails are rarely displayed at such.  I am not sure if this is due to something non-standard in the email itself, or a bug in the mail client. (UPDATE:  This is actually an issue with Microsoft Exchange ActiveSync 2003.  The 2007 version will sync HTML emails without converting to plain text.)
• Emails cannot be rotated to the landscape position.
• There really need to be some sort of shortcut keys to get to the top or bottom of long emails or lists of emails.

  The Browser

• Overall it seems to work pretty well, and is a definite improvement when compared to the browser in the Treo line.
• I know this is 'coming soon', but Flash and Java support are definitely needed ASAP.
• While the browser does work great in rotated mode, there is no facility to enter text in that mode (that I have found).  What we really need is a popup keyboard that can be summoned when in landscape mode or if the keyboard is closed.  This keyboard should really be available anywhere, but I listed it here because this is where I seemed to long for it the most.

  The webOS

• Similar to the mail client, the UI seems to be a little less than complete.  Everything works, but there are a few options and features that have been omitted.  Nothing major, but that can still be a pain once you realize you don't have them.
• The Launcher is one area that although it works, it just begs for some customization options.  There seems to be no rhyme or reason to the way icons are added to the various Launcher pages.  Currently my 1st page has way too many icons, and the 2nd and 3rd page are not even full yet.  Not sure what they were trying to do, but some way of organizing icons and breaking them into folders or groups is an absolute must.
• And speaking of the Launcher, am I the only one who has not found a way to delete a contact from the list? (UPDATE:  I was not the only one.  Luckily, it was actually just something I overlooked in the documentation.  Press and hold the Orange button while selecting the icon in the Launcher.  The Pre will prompt you to delete the icon.) 
• The screen lock function is nice, but it really should be configurable to less than 4 digits if desired.  If the only reason you lock the screen is to avoid accidental dialing, a simpler screen unlock would be nice.  The really big negative on the screen lock is that the only two ways I have found to make it appear are sliding out the keyboard or plugging in USB.  It should also display when you press one of the external buttons too, so you do not need to open the keyboard. (UPDATE:  Yet another case of not paying enough attention to the docs (RTFM)...  The power button is actually named the power/wake button.  Doh!)

  The Phone & Contacts

• Believe it or not, there are speed dials on the Pre.  They did a masterful job of hiding them inside Contacts, and even there in a submenu.  The list should be available or at least visible in the phone app.
• Contacts all have a nice gray placeholder for the person's photo, but I do not see any way to actually set a photo.  A bit of a tease, if you ask me.
• Also in Contacts, you have the option to add a Contact to the Launcher.  I had hoped this would be a 'one-touch speed dial', but all it actually does is link back to the entire Contact card.  

  The App Store

• We all expected the App Store to be limited on launch, so no real complaints there.  I would like the apps to list price/licensing details.  Not that any of us are really going to buy 'Connect 4' anyhow, but if we knew it cost money then we could save the download.

Wrap-up

I know this sounds like a lot of negativity, but I have to stress that I am still very impressed with the Pre overall.  Almost every issue I have had so far seems like a software deficiency, not a hardware problem.  That means that most or all can probably be addressed with OTA updates and we will not be forced to wait for the Pre2.