A similar patch has just gone into beagle, which provides better
compatibility with both libexif 0.5 and 0.6.

Index: configure.in
===================================================================
RCS file: /cvs/gnome/f-spot/configure.in,v
retrieving revision 1.48
diff -u -B -r1.48 configure.in
--- configure.in	16 Feb 2005 23:46:00 -0000	1.48
+++ configure.in	19 Feb 2005 15:58:22 -0000
@@ -48,6 +48,7 @@
 LIBGNOMEUI_REQUIRED=2.2
 LIBEXIF_REQUIRED_MIN=0.5.7
 LIBEXIF_REQUIRED_MAX=0.7.0
+LIBEXIF_API_CHANGE=0.6.0
 GTKSHARP_REQUIRED=1.0
 
 dnl -- this check is 	
@@ -58,6 +59,14 @@
 AC_SUBST(F_CFLAGS)
 AC_SUBST(F_LIBS)
 
+PKG_CHECK_MODULES(LIBEXIF_API_CHECK, libexif >= $LIBEXIF_API_CHANGE, have_old_libexif=no, have_old_libexif=yes)
+if test "$have_old_libexif" = "yes"; then
+	CSFLAGS="-define:HAVE_OLD_LIBEXIF"
+else
+	CSFLAGS=""
+fi
+
+AC_SUBST(CSFLAGS)
 
 dnl --- GConf
 
Index: src/Exif.cs
===================================================================
RCS file: /cvs/gnome/f-spot/src/Exif.cs,v
retrieving revision 1.6
diff -u -B -r1.6 Exif.cs
--- src/Exif.cs	29 Jan 2005 21:41:34 -0000	1.6
+++ src/Exif.cs	19 Feb 2005 15:58:22 -0000
@@ -657,27 +657,22 @@
 		}
 		
 		
-		// FIXME this version is only valid in libexif 0.5
 		[DllImport ("libexif.dll")]
+#if HAVE_OLD_LIBEXIF
 		internal static extern IntPtr exif_entry_get_value (HandleRef handle);
-		
-		// FIXME this version is only valid in libexif 0.6
-		[DllImport ("libexif.dll")]
+#else
 		internal static extern IntPtr exif_entry_get_value (HandleRef handle, byte  [] value, int maxlen);
+#endif
 		
 		public string Value
 		{
 			get {
-				// FIXME this is a hack to handle libexif 0.5 and 0.6 at the same time
-				// The signature of get_value changed between versions
-				
-				try {
-					return Marshal.PtrToStringAnsi (exif_entry_get_value (this.Handle));
-				} catch (System.NullReferenceException e) {
-					byte [] value = new byte [1024];
-					exif_entry_get_value (this.Handle, value, value.Length);
-					return System.Text.Encoding.UTF8.GetString (value);
-				}
+#if HAVE_OLD_LIBEXIF
+				return Marshal.PtrToStringAnsi (exif_entry_get_value (this.Handle));
+#else
+				byte [] value = new byte [1024];
+				return Marshal.PtrToStringAnsi (exif_entry_get_value (this.Handle, value, value.Length));
+#endif
 			}
 		}
 		
Index: src/ExifData.cs
===================================================================
RCS file: /cvs/gnome/f-spot/src/ExifData.cs,v
retrieving revision 1.13
diff -u -B -r1.13 ExifData.cs
--- src/ExifData.cs	24 Jan 2005 08:53:14 -0000	1.13
+++ src/ExifData.cs	19 Feb 2005 15:58:22 -0000
@@ -238,13 +238,12 @@
 	readonly public uint  size;
 	readonly public _ExifContent *parent;
 
-	// FIXME this version is only valid in libexif 0.5
 	[DllImport ("libexif.dll")]
+#if HAVE_OLD_LIBEXIF
 	internal static extern IntPtr exif_entry_get_value (_ExifEntry *entry);
-
-	// FIXME this version is only valid in libexif 0.6
-	[DllImport ("libexif.dll")]
-	internal static extern IntPtr exif_entry_get_value (_ExifEntry *entry, byte  [] value, int maxlen);	
+#else
+	internal static extern IntPtr exif_entry_get_value (_ExifEntry *entry, byte  [] value, int maxlen);
+#endif
 
 }
 
@@ -370,16 +369,12 @@
 
 	unsafe string GetStringValue (_ExifEntry *entry)
 	{
-		// FIXME this is a hack to handle libexif 0.5 and 0.6 at the same time
-		// The signature of get_value changed between versions
-
-		try {
-			return Marshal.PtrToStringAnsi (_ExifEntry.exif_entry_get_value (entry));
-		} catch (System.NullReferenceException e) {
-			byte [] value = new byte [1024];
-			_ExifEntry.exif_entry_get_value (entry, value, value.Length);
-			return System.Text.Encoding.UTF8.GetString (value);
-		}
+#if HAVE_OLD_LIBEXIF
+		return Marshal.PtrToStringAnsi (_ExifEntry.exif_entry_get_value (entry));
+#else
+		byte [] value = new byte [1024];
+		return Marshal.PtrToStringAnsi (_ExifEntry.exif_entry_get_value (entry, value, value.Length));
+#endif
 	}
 
 	unsafe void AssembleContent (_ExifEntry *entry, void *callback_data)