Share your experience!
Hy!
After the upgrade (all went well), when I select a contactI have the same number several times on the screen.
If I choose edit, in the edit menu are same numbers gor google, sony sync and phone contacts. Even if I try to filter them, they are there.
Thanks.
This is common but don't worry it has a fix. 
Please go to your phonebook and press the menu button, then select settings > accounts & sync > From here you will only select one account to sync with because when you sync different accounts it will duplicate the contacts and will affect your phonebook.
You should also filter them from the phonebook by pressing the option next to the search bar with 3 faces (first option on the top left of your screen).
Please use this two options to filter it as you would like.
Actually, the X8 doesn't have the 3 faces (at least mine doesn't) but the menu button brings up various choices, and by pressing 'Contacts to view' you can filter what is shown in the contacts list. It might take a bit of playing around, but you will be able to hide some of the numbers from the list...
Thank you Tony, thank you sushi,
As there is always a "but", I have to mention just a few of them:
1. I can't select Sony as the only account to sync with, because google is there by default; I think is there because Android Market asked about it first time when tried to access it
2. no search bar with three faces 
3. the filter contact does not work; I can make them all dissapear (by not selecting any of the options for google, phone or sonysync) but when I select at least one option from any of them, all the tripled contacts will appear
I've noticed this behaviour after upgrading. With 1.6 version I had only one contact that appears.
Still to work on this
Do your contacts in Google differ from your Phone Contacts slightly? Such as having the country code in front (eg. +123) or in Google Contacts, are there those little dashes in between the numbers? eg.123-4567-89
Because when I exported the Phone Contacts to memory card as a vcard and then imported it into Google Contacts, the numbers had those little dashes. And when I sync the phone with Google, they appear as 2 numbers. But if I edit the number in Google and remove the dashes, so that they are now identical with my Phone Contact (eg. 123456789) then they appear as one number.
Yes, in 1.6 I didn't have this problem, and the ''Choose Contacts To View'' options worked well.
Also, in 1.6 I somehow managed to upload my phone contacts to Google just by syncing (not by exporting and importing vcard) but now it doesn't seem to work in 2.1.
Similarly encountered this one -- multiple same numbers and other entries appearing in a single contact -- after restoring from a backup. Trying out the filters and sync didn't work. What i did instead was do "factory data reset", from settings>privacy. After restarting, I did a "backup restore" and all went well.
What you'll notice here is HOW EASY IT IS DO factory data reset, how easy it is to erase all existing data in your phone too!!! Such that an errant person who happens to get hold of your phone, can do a total disaster just out of curiousity....
same issue after i updated my phone i only have like 3 numbers on my phonebook. when i tried to sync,everything went double and all of the contacts of my friends are there. i just noticed that most of the numbers are either from facebook/gmail.but i like it coz i dont have have to type / copy all of it all over again.
Cheers! :smileygrin:
Even if after "Factory reset" all is well, after first "sync" (google or sony), multiple contacts re-appear.