My Mac2010 MacBook under Leopard had 4 partitions:
Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
------------------------------------------------------------------
 Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          26      204819+  ee  GPT   << EFI boot chooser
/dev/sda2   *          26        9670    77463552   af  HFS / HFS+ << MAC
/dev/sda3            9670       16044    51196928   83  Linux  << Ubuntu
/dev/sda4           16044       19458    27423744    b  W95 FAT32 << common storage

The installer-Lion upgrade failed, without useful details.
Eventually the problem proved to be that the upgrade wants to create a small Recovery Partition,
while the GPT disk only supports 4 partitions. Thus one had to be first sacrificed to run the upgrade.

After saving data files, /etc/apt, & /etc/fstab , I deleted the Linux partition with Gparted. The installer-Lion upgrade was then trouble free, with the vfat  Recovery Partition just behind the Mac partition

http://support.apple.com/kb/HT4848  instructs how to transnd then to reinstall Ubuntu,
with essentially the same final disk structure as above.  Therefrom under Ubuntu, this email is sent.

Minor aside.  
========== ===
The USB Recovery supported bootup when the Option key was 
pressed. Also the EFI boot chooser recognized this USB.  Here is the USB info:

$ mount /dev/sdb1
/dev/sdb1 on /media/Recovery HD type hfsplus (rw,nosuid,nodev,uhelper=udisks)

$ df /dev/sdb1
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sdb1               634768    488112    146656  77% /media/Recovery HD
on a 2 Gig USB stick

$ ls -lh /media/"Recovery HD"
total 0
drwxr-xr-x 1 root root 10 2011-08-19 10:59 com.apple.recovery.boot

$ ls -lh /media/"Recovery HD"/com.apple.recovery.boot
total 455M
-rw-r--r-- 1 root   80 1.9K 2011-06-30 02:55 BaseSystem.chunklist
-rw-r--r-- 1 root   80 431M 2011-06-30 02:47 BaseSystem.dmg
-rw-r--r-- 1 root root 839K 2011-06-30 02:04 boot.efi
-rw-r--r-- 1 root root  361 2011-08-19 10:59 com.apple.Boot.plist
-rw-r--r-- 1 root root  23M 2011-06-30 01:41 kernelcache
-rw-r--r-- 1 root root 2.2K 2011-06-15 21:06 PlatformSupport.plist
-r--r--r-- 1 root root  475 2011-06-29 23:42 SystemVersion.plist

Another USB stick boot competent on PCs failed on the MAC, so the hfsplus formatting is necessary.
Has anyone made a USB with Linux bootable on MACs?

MarvS