Moving SPI pin initialization from constructor to begin() function. That way, the SPI library won't alter any pin states unless / until you call begin().

libraries/Ethernet/examples/BarometricPressureWebServer/BarometricPressureWebServer.pde

@@ -60,6 +60,9 @@ long pressure = 0;
 long lastReadingTime = 0;
 
 void setup() {
+  // start the SPI library:
+  SPI.begin();
+
   // start the Ethernet connection and the server:
   Ethernet.begin(mac, ip);
   server.begin();
@@ -68,8 +71,6 @@ void setup() {
   pinMode(dataReadyPin, INPUT);
   pinMode(chipSelectPin, OUTPUT);
 
-  // start the SPI library:
-  SPI.begin();
   Serial.begin(9600);
 
   //Configure SCP1000 for low noise configuration:

libraries/Ethernet/utility/w5100.cpp

@@ -25,8 +25,11 @@ W5100Class W5100;
 
 void W5100Class::init(void)
 {
-  initSS();
+  delay(300);
 
+  SPI.begin();
+  initSS();
+  
   writeMR(1<<RST);
   writeTMSR(0x55);
   writeRMSR(0x55);

libraries/SPI/SPI.cpp

@@ -13,8 +13,7 @@
 
 SPIClass SPI;
 
-SPIClass::SPIClass()
-{
+void SPIClass::begin() {
   // Set direction register for SCK and MOSI pin.
   // MISO pin automatically overrides to INPUT.
   // When the SS pin is set as OUTPUT, it can be used as
@@ -29,12 +28,15 @@ SPIClass::SPIClass()
   digitalWrite(MOSI, LOW);
   digitalWrite(SS, HIGH);
 
-  SPCR  = _BV(SPE) | _BV(MSTR);
-  
   // Warning: if the SS pin ever becomes a LOW INPUT then SPI 
   // automatically switches to Slave, so the data direction of 
   // the SS pin MUST be kept as OUTPUT.
-  SPCR  = _BV(SPE) | _BV(MSTR);
+  SPCR |= _BV(MSTR);
+  SPCR |= _BV(SPE);
+}
+
+void SPIClass::end() {
+  SPCR &= ~_BV(SPE);
 }
 
 void SPIClass::setBitOrder(uint8_t bitOrder)

libraries/SPI/SPI.h

@@ -35,8 +35,6 @@
 
 class SPIClass {
 public:
-  SPIClass();
-
   inline static byte transfer(byte _data);
 
   // SPI Configuration methods
@@ -44,8 +42,8 @@ public:
   inline static void attachInterrupt();
   inline static void detachInterrupt(); // Default
 
-  inline static void begin(); // Default
-  inline static void end();
+  static void begin(); // Default
+  static void end();
 
   static void setBitOrder(uint8_t);
   static void setDataMode(uint8_t);
@@ -69,12 +67,4 @@ void SPIClass::detachInterrupt() {
   SPCR &= ~_BV(SPIE);
 }
 
-void SPIClass::begin() {
-  SPCR |= _BV(SPE);
-}
-
-void SPIClass::end() {
-  SPCR &= ~_BV(SPE);
-}
-
 #endif

libraries/SPI/examples/BarometricPressureSensor/BarometricPressureSensor.pde

@@ -36,13 +36,14 @@ const int chipSelectPin = 7;
 
 void setup() {
   Serial.begin(9600);
-  // initalize the  data ready and chip select pins:
-  pinMode(dataReadyPin, INPUT);
-  pinMode(chipSelectPin, OUTPUT);
 
   // start the SPI library:
   SPI.begin();
 
+  // initalize the  data ready and chip select pins:
+  pinMode(dataReadyPin, INPUT);
+  pinMode(chipSelectPin, OUTPUT);
+
   //Configure SCP1000 for low noise configuration:
   writeRegister(0x02, 0x2D);
   writeRegister(0x01, 0x03);